In mathematics, a plane is a two-dimensional manifold or surface that is perfectly flat. Informally, it can be thought of as an infinitely vast and infinitesimally thin sheet oriented in some space. Formally, it is an affine space of dimension two.
When working in two-dimensional Euclidean space, the definite article is used, the plane, to refer to the whole space. Many fundamental tasks in geometry, trigonometry, and graphing are performed in two-dimensional space, or in other words, in the plane. A lot of mathematics can be and has been performed in the plane, notably in the areas of geometry, trigonometry, graph theory and graphing. All two-dimensional figures are assumed to be on a plane, even on the plane, unless otherwise specified.
Contents
[hide]
* 1 Euclidean geometry
o 1.1 Orientation
* 2 Planes embedded in R3
o 2.1 Properties
o 2.2 Define a plane with a point and a normal vector
o 2.3 Define a plane through three points
o 2.4 Distance from a point to a plane
o 2.5 Line of intersection between two planes
o 2.6 Dihedral angle
* 3 Planes in various areas of mathematics
* 4 Planes in Fiction
* 5 See also
* 6 External links
[edit] Euclidean geometry
In Euclidean space a plane is a surface such that, given any two distinct points on the surface, the surface also contains the unique straight line that passes through those points.
The fundamental structure of two such planes will always be the same. In mathematics this is described as topological equivalence. Informally though, it means that any two planes look the same.
A plane can be uniquely determined by any of the following (sets of) objects:
* three non-collinear points (i.e., not lying on the same line)
* a line and a point not on the line
* two lines with one point of intersection
* two parallel lines
[edit] Orientation
Three parallel planes.
Three parallel planes.
Like lines, planes can be parallel or intersecting. Differing from lines, however, planes cannot be skew. Lines drawn on two parallel planes will either be parallel or skew, but will not intersect. Intersecting planes may be perpendicular, or may form any number of other angles.
[edit] Planes embedded in R3
This section is specifically concerned with planes embedded in three dimensions: specifically, in ℝ3.
[edit] Properties
In three-dimensional Euclidean space, we may exploit the following facts that do not hold in higher dimensions:
* Two planes are either parallel or they intersect in a line.
* A line is either parallel to a plane or intersects it at a single point or is contained in the plane.
* Two lines perpendicular to the same plane must be parallel to each other.
* Two planes perpendicular to the same line must be parallel to each other.
[edit] Define a plane with a point and a normal vector
In a three-dimensional space, another important way of defining a plane is by specifying a point and a normal vector to the plane.
Let \bold p be the point we wish to lie in the plane, and let \vec n be a nonzero normal vector to the plane. The desired plane is the set of all points \bold r such that \vec n\cdot (r-\bold p)=0.
If we write \vec n = \begin{bmatrix}a\\ b\\ c\end{bmatrix} , \bold r = (x, y, z) and d as the dot product \vec n\cdot \bold p=-d, then the plane Π is determined by the condition ax + by + cz + d = 0\,, where a, b, c and d are real numbers and a,b, and c are not all zero.
Alternatively, a plane may be described parametrically as the set of all points of the form \vec{u} + s\vec{v} + t\vec{w}, where s and t range over all real numbers, and \vec{u}, \vec{v} and \vec{w} are given vectors defining the plane. \vec{u} points from the origin to an arbitrary point on the plane, and \vec{v} and \vec{w} can be visualized as starting at \vec{u} and pointing in different directions along the plane. \vec{v} and \vec{w} can, but do not have to be perpendicular (but they cannot be collinear).
[edit] Define a plane through three points
* The plane passing through three points \bold p_1 = (x_1,y_1,z_1) , \bold p_2 = (x_2,y_2,z_2) and \bold p_3 = (x_3,y_3,z_3) can be defined as the set of all points (x,y,z) that satisfy the following determinant equations:
\begin{vmatrix} x - x_1 & y - y_1 & z - z_1 \\ x_2 - x_1 & y_2 - y_1& z_2 - z_1 \\ x_3 - x_1 & y_3 - y_1 & z_3 - z_1 \end{vmatrix} =\begin{vmatrix} x - x_1 & y - y_1 & z - z_1 \\ x - x_2 & y - y_2 & z - z_2 \\ x - x_3 & y - y_3 & z - z_3 \end{vmatrix} = 0.
* To describe the plane as an equation in the form ax + by + cz + d = 0, solve the following system of equations:
\, ax_1 + by_1 + cz_1 + d = 0
\, ax_2 + by_2 + cz_2 + d = 0
\, ax_3 + by_3 + cz_3 + d = 0.
This system can be solved using Cramer's Rule and basic matrix manipulations. Let D = \begin{vmatrix} x_1 & y_1 & z_1 \\ x_2 & y_2 & z_2 \\ x_3 & y_3 & z_3 \end{vmatrix}. Then,
a = \frac{-d}{D} \begin{vmatrix} 1 & y_1 & z_1 \\ 1 & y_2 & z_2 \\ 1 & y_3 & z_3 \end{vmatrix}
b = \frac{-d}{D} \begin{vmatrix} x_1 & 1 & z_1 \\ x_2 & 1 & z_2 \\ x_3 & 1 & z_3 \end{vmatrix}
c = \frac{-d}{D} \begin{vmatrix} x_1 & y_1 & 1 \\ x_2 & y_2 & 1 \\ x_3 & y_3 & 1 \end{vmatrix}.
These equations are parametric in d. Setting d equal to any non-zero number and substituting it into these equations will yield one solution set.
* This plane can also be described by the "point and a normal vector" prescription above.
A suitable normal vector is given by the cross product \vec n = ( \bold p_2 - \bold p_1 ) \times ( \bold p_3 - \bold p_1 ), and the point \bold p can be taken to be any of given points \bold p_1, \bold p_2 or \bold p_3.
[edit] Distance from a point to a plane
For a plane \Pi : ax + by + cz + d = 0\, and a point \bold p_1 = (x_1,y_1,z_1) not necessarily lying on the plane, the shortest distance from \bold p_1 to the plane is
D = \frac{\left | a x_1 + b y_1 + c z_1+d \right |}{\sqrt{a^2+b^2+c^2}}.
It follows that \bold p_1 lies in the plane if and only if D=0.
If \sqrt{a^2+b^2+c^2}=1 meaning that a, b and c are normalized then the equation becomes
D = \ | a x_1 + b y_1 + c z_1+d | .
[edit] Line of intersection between two planes
Given intersecting planes described by \Pi_1 : \vec n_1\cdot \bold r = h_1 and \Pi_2 : \vec n_2\cdot \bold r = h_2, the line of intersection is perpendicular to both \vec n_1 and \vec n_2 and thus parallel to \vec n_1 \times \vec n_2 . This cross product is zero only if the planes are parallel, and are therefore non-intersecting or coincident.
Any point in space may be written as \bold r = c_1\vec n_1 + c_2\vec n_2 + c_3(\vec n_1 \times \vec n_2), since \{ \vec n_1, \vec n_2, (\vec n_1 \times \vec n_2) \} is a basis. In this equation, c3 is the line's parameter, and c1 and c2 are constants. By taking the dot product of this equation against \vec n_1 and \vec n_2, and by noting that \vec n_i \cdot \bold r = h_i, we obtain two scalar equations that may be solved for {c1,c2}.
If we further assume that \vec n_1 and \vec n_2 are orthonormal then the closest point on the line of intersection to the origin is \bold r_0 = h_1\vec n_1 + h_2\vec n_2 .
[edit] Dihedral angle
Given two intersecting planes described by \Pi_1 : a_1 x + b_1 y + c_1 z + d_1 = 0\, and \Pi_2 : a_2 x + b_2 y + c_2 z + d_2 = 0\,, the dihedral angle between them is defined to be the angle α between their normal directions:
\cos\alpha = \hat n_1\cdot \hat n_2 = \frac{a_1 a_2 + b_1 b_2 + c_1 c_2}{\sqrt{a_1^2+b_1^2+c_1^2}\sqrt{a_2^2+b_2^2+c_2^2}}.
[edit] Planes in various areas of mathematics
In addition to its familiar geometric structure, with isomorphisms that are isometries with respect to the usual inner product, the plane may be viewed at various other levels of abstraction. Each level of abstraction corresponds to a specific category.
At one extreme, all geometrical and metric concepts may be dropped to leave the topological plane, which may be thought of as an idealised homotopically trivial infinite rubber sheet, which retains a notion of proximity, but has no distances. The topological plane has a concept of a linear path, but no concept of a straight line. The topological plane, or its equivalent the open disc, is the basic topological neighbourhood used to construct surfaces (or 2-manifolds) classified in low-dimensional topology. Isomorphisms of the topological plane are all continuous bijections. The topological plane is the natural context for the branch of graph theory that deals with planar graphs, and results such as the four color theorem.
The plane may also be viewed as an affine space, whose isomorphisms are combinations of translations and non-singular linear maps. From this viewpoint there are no distances, but colinearity and ratios of distances on any line are preserved.
Differential geometry views a plane as a 2-dimensional real manifold, a topological plane which is provided with a differential structure. Again in this case, there is no notion of distance, but there is now a concept of smoothness of maps, for example a differentiable or smooth path (depending on the type of differential structure applied). The isomorphisms in this case are bijections with the chosen degree of differentiability.
In the opposite direction of abstraction, we may apply a compatible field structure to the geometric plane, giving rise to the complex plane and the major area of complex analysis. The complex field has only two isomorphisms that leave the real line fixed, the identity and conjugation.
In the same way as in the real case, the plane may also be viewed as the simplest, one-dimensional (over the complex numbers) complex manifold, sometimes called the complex line. However, this viewpoint contrasts sharply with the case of the plane as a 2-dimensional real manifold. The isomorphisms are all conformal bijections of the complex plane, but the only possibilities are maps that correspond to the composition of a multiplication by a complex number and a translation.
In addition, the Euclidean geometry (which has zero curvature everywhere) is not the only geometry that the plane may have. The plane may be given a spherical geometry by using the stereographic projection. This can be thought of as placing a sphere on the plane (just like a ball on the floor), removing the top point, and projecting the sphere onto the plane from this point). This is one of the projections that may be used in making a flat map of part of the Earth's surface. The resulting geometry has constant positive curvature.
Alternatively, the plane can also be given a metric which gives it constant negative curvature giving the hyperbolic plane. The latter possibility finds an application in the theory of special relativity in the simplified case where there are two spatial dimensions and one time dimension. (The hyperbolic plane is a timelike hypersurface in three-dimensional Minkowski space.)
[edit] Planes in Fiction
The 1884 novel Flatland by Edwin A. Abbott features the concept of a geometric, two dimensional infinite plane inhabited by living geometric figures (triangles, squares, circles, etc.). It has been described by Isaac Asimov, in his foreword to the Signet Classics 1984 edition, as "the best introduction one can find into the manner of perceiving dimensions."
[edit] See also
* Half-plane
* Hyperplane
* Line-plane intersection
* Point on plane closest to origi
Tuesday, July 15, 2008
Computer
A computer is a machine that manipulates data according to a list of instructions.
The first devices that resemble modern computers date to the mid-20th century (around 1940 - 1945), although the computer concept and various machines similar to computers existed earlier. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers.[1] Modern computers are based on tiny integrated circuits and are millions to billions of times more capable while occupying a fraction of the space.[2] Today, simple computers may be made small enough to fit into a wristwatch and be powered from a watch battery. Personal computers, in various forms, are icons of the Information Age and are what most people think of as "a computer"; however, the most common form of computer in use today is the embedded computer. Embedded computers are small, simple devices that are used to control other devices — for example, they may be found in machines ranging from fighter aircraft to industrial robots, digital cameras, and children's toys.
The ability to store and execute lists of instructions called programs makes computers extremely versatile and distinguishes them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, computers with capability and complexity ranging from that of a personal digital assistant to a supercomputer are all able to perform the same computational tasks given enough time and storage capacity.
Contents
[hide]
* 1 History of computing
* 2 Stored program architecture
o 2.1 Programs
o 2.2 Example
* 3 How computers work
o 3.1 Control unit
o 3.2 Arithmetic/logic unit (ALU)
o 3.3 Memory
o 3.4 Input/output (I/O)
o 3.5 Multitasking
o 3.6 Multiprocessing
o 3.7 Networking and the Internet
* 4 Further topics
o 4.1 Hardware
o 4.2 Software
o 4.3 Programming languages
o 4.4 Professions and organizations
* 5 See also
* 6 Notes
* 7 References
History of computing
Main article: History of computer hardware
The Jacquard loom was one of the first programmable devices.
The Jacquard loom was one of the first programmable devices.
It is difficult to identify any one device as the earliest computer, partly because the term "computer" has been subject to varying interpretations over time. Originally, the term "computer" referred to a person who performed numerical calculations (a human computer), often with the aid of a mechanical calculating device.
The history of the modern computer begins with two separate technologies - that of automated calculation and that of programmability.
Examples of early mechanical calculating devices included the abacus, the slide rule and arguably the astrolabe and the Antikythera mechanism (which dates from about 150-100 BC). The end of the Middle Ages saw a re-invigoration of European mathematics and engineering, and Wilhelm Schickard's 1623 device was the first of a number of mechanical calculators constructed by European engineers. However, none of those devices fit the modern definition of a computer because they could not be programmed.
Hero of Alexandria (c. 10 – 70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions - and when.[3] This is the essence of programmability. In 1801, Joseph Marie Jacquard made an improvement to the textile loom that used a series of punched paper cards as a template to allow his loom to weave intricate patterns automatically. The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven patterns can be viewed as an early, albeit limited, form of programmability.
It was the fusion of automatic calculation with programmability that produced the first recognizable computers. In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer that he called "The Analytical Engine".[4] Due to limited finances, and an inability to resist tinkering with the design, Babbage never actually built his Analytical Engine.
Large-scale automated data processing of punched cards was performed for the U.S. Census in 1890 by tabulating machines designed by Herman Hollerith and manufactured by the Computing Tabulating Recording Corporation, which later became IBM. By the end of the 19th century a number of technologies that would later prove useful in the realization of practical computers had begun to appear: the punched card, Boolean algebra, the vacuum tube (thermionic valve) and the teleprinter.
During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.
Defining characteristics of some early digital computers of the 1940s (In the history of computing hardware) Name First operational Numeral system Computing mechanism Programming Turing complete
Zuse Z3 (Germany) May 1941 Binary Electro-mechanical Program-controlled by punched film stock Yes (1998)
Atanasoff–Berry Computer (USA) Summer 1941 Binary Electronic Not programmable—single purpose No
Colossus (UK) January 1944 Binary Electronic Program-controlled by patch cables and switches No
Harvard Mark I – IBM ASCC (USA) 1944 Decimal Electro-mechanical Program-controlled by 24-channel punched paper tape (but no conditional branch) Yes (1998)
ENIAC (USA) November 1945 Decimal Electronic Program-controlled by patch cables and switches Yes
Manchester Small-Scale Experimental Machine (UK) June 1948 Binary Electronic Stored-program in Williams cathode ray tube memory Yes
Modified ENIAC (USA) September 1948 Decimal Electronic Program-controlled by patch cables and switches plus a primitive read-only stored programming mechanism using the Function Tables as program ROM Yes
EDSAC (UK) May 1949 Binary Electronic Stored-program in mercury delay line memory Yes
Manchester Mark I (UK) October 1949 Binary Electronic Stored-program in Williams cathode ray tube memory and magnetic drum memory Yes
CSIRAC (Australia) November 1949 Binary Electronic Stored-program in mercury delay line memory Yes
A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features that are seen in modern computers. The use of digital electronics (largely invented by Claude Shannon in 1937) and more flexible programmability were vitally important steps, but defining one point along this road as "the first digital electronic computer" is difficult (Shannon 1940). Notable achievements include:
EDSAC was one of the first computers to implement the stored program (von Neumann) architecture.
EDSAC was one of the first computers to implement the stored program (von Neumann) architecture.
* Konrad Zuse's electromechanical "Z machines". The Z3 (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability. In 1998 the Z3 was proved to be Turing complete, therefore being the world's first operational computer.
* The non-programmable Atanasoff–Berry Computer (1941) which used vacuum tube based computation, binary numbers, and regenerative capacitor memory.
* The secret British Colossus computers (1943)[5], which had limited programmability but demonstrated that a device using thousands of tubes could be reasonably reliable and electronically reprogrammable. It was used for breaking German wartime codes.
* The Harvard Mark I (1944), a large-scale electromechanical computer with limited programmability.
* The U.S. Army's Ballistics Research Laboratory ENIAC (1946), which used decimal arithmetic and is sometimes called the first general purpose electronic computer (since Konrad Zuse's Z3 of 1941 used electromagnets instead of electronics). Initially, however, ENIAC had an inflexible architecture which essentially required rewiring to change its programming.
Several developers of ENIAC, recognizing its flaws, came up with a far more flexible and elegant design, which came to be known as the "stored program architecture" or von Neumann architecture. This design was first formally described by John von Neumann in the paper First Draft of a Report on the EDVAC, distributed in 1945. A number of projects to develop computers based on the stored-program architecture commenced around this time, the first of these being completed in Great Britain. The first to be demonstrated working was the Manchester Small-Scale Experimental Machine (SSEM or "Baby"), while the EDSAC, completed a year after SSEM, was the first practical implementation of the stored program design. Shortly thereafter, the machine originally described by von Neumann's paper—EDVAC—was completed but did not see full-time use for an additional two years.
Nearly all modern computers implement some form of the stored-program architecture, making it the single trait by which the word "computer" is now defined. While the technologies used in computers have changed dramatically since the first electronic, general-purpose computers of the 1940s, most still use the von Neumann architecture.
Microprocessors are miniaturized devices that often implement stored program CPUs.
Microprocessors are miniaturized devices that often implement stored program CPUs.
Computers that used vacuum tubess as their electronic elements were in use throughout the 1950s. Vacuum tube electronics were largely replaced in the 1960s by transistor-based electronics, which are smaller, faster, cheaper to produce, require less power, and are more reliable. In the 1970s, integrated circuit technology and the subsequent creation of microprocessors, such as the Intel 4004, further decreased size and cost and further increased speed and reliability of computers. By the 1980s, computers became sufficiently small and cheap to replace simple mechanical controls in domestic appliances such as washing machines. The 1980s also witnessed home computers and the now ubiquitous personal computer. With the evolution of the Internet, personal computers are becoming as common as the television and the telephone in the household.
Stored program architecture
Main articles: Computer program and Computer programming
The defining feature of modern computers which distinguishes them from all other machines is that they can be programmed. That is to say that a list of instructions (the program) can be given to the computer and it will store them and carry them out at some time in the future.
In most cases, computer instructions are simple: add one number to another, move some data from one location to another, send a message to some external device, etc. These instructions are read from the computer's memory and are generally carried out (executed) in the order they were given. However, there are usually specialized instructions to tell the computer to jump ahead or backwards to some other place in the program and to carry on executing from there. These are called "jump" instructions (or branches). Furthermore, jump instructions may be made to happen conditionally so that different sequences of instructions may be used depending on the result of some previous calculation or some external event. Many computers directly support subroutines by providing a type of jump that "remembers" the location it jumped from and another instruction to return to the instruction following that jump instruction.
Program execution might be likened to reading a book. While a person will normally read each word and line in sequence, they may at times jump back to an earlier place in the text or skip sections that are not of interest. Similarly, a computer may sometimes go back and repeat the instructions in some section of the program over and over again until some internal condition is met. This is called the flow of control within the program and it is what allows the computer to perform tasks repeatedly without human intervention.
Comparatively, a person using a pocket calculator can perform a basic arithmetic operation such as adding two numbers with just a few button presses. But to add together all of the numbers from 1 to 1,000 would take thousands of button presses and a lot of time—with a near certainty of making a mistake. On the other hand, a computer may be programmed to do this with just a few simple instructions. For example:
mov #0,sum ; set sum to 0
mov #1,num ; set num to 1
loop: add num,sum ; add num to sum
add #1,num ; add 1 to num
cmp num,#1000 ; compare num to 1000
ble loop ; if num <= 1000, go back to 'loop'
halt ; end of program. stop running
Once told to run this program, the computer will perform the repetitive addition task without further human intervention. It will almost never make a mistake and a modern PC can complete the task in about a millionth of a second.[6]
However, computers cannot "think" for themselves in the sense that they only solve problems in exactly the way they are programmed to. An intelligent human faced with the above addition task might soon realize that instead of actually adding up all the numbers one can simply use the equation
1+2+3+...+n = {{n(n+1)} \over 2}
and arrive at the correct answer (500,500) with little work.[7] In other words, a computer programmed to add up the numbers one by one as in the example above would do exactly that without regard to efficiency or alternative solutions.
Programs
A 1970s punched card containing one line from a FORTRAN program. The card reads: "Z(1) = Y + W(1)" and is labelled "PROJ039" for identification purposes.
A 1970s punched card containing one line from a FORTRAN program. The card reads: "Z(1) = Y + W(1)" and is labelled "PROJ039" for identification purposes.
In practical terms, a computer program may run from just a few instructions to many millions of instructions, as in a program for a word processor or a web browser. A typical modern computer can execute billions of instructions per second (gigahertz or GHz) and rarely make a mistake over many years of operation. Large computer programs comprising several million instructions may take teams of programmers years to write, thus the probability of the entire program having been written without error is highly unlikely.
Errors in computer programs are called "bugs". Bugs may be benign and not affect the usefulness of the program, or have only subtle effects. But in some cases they may cause the program to "hang" - become unresponsive to input such as mouse clicks or keystrokes, or to completely fail or "crash". Otherwise benign bugs may sometimes may be harnessed for malicious intent by an unscrupulous user writing an "exploit" - code designed to take advantage of a bug and disrupt a program's proper execution. Bugs are usually not the fault of the computer. Since computers merely execute the instructions they are given, bugs are nearly always the result of programmer error or an oversight made in the program's design.[8]
In most computers, individual instructions are stored as machine code with each instruction being given a unique number (its operation code or opcode for short). The command to add two numbers together would have one opcode, the command to multiply them would have a different opcode and so on. The simplest computers are able to perform any of a handful of different instructions; the more complex computers have several hundred to choose from—each with a unique numerical code. Since the computer's memory is able to store numbers, it can also store the instruction codes. This leads to the important fact that entire programs (which are just lists of instructions) can be represented as lists of numbers and can themselves be manipulated inside the computer just as if they were numeric data. The fundamental concept of storing programs in the computer's memory alongside the data they operate on is the crux of the von Neumann, or stored program, architecture. In some cases, a computer might store some or all of its program in memory that is kept separate from the data it operates on. This is called the Harvard architecture after the Harvard Mark I computer. Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in CPU caches.
While it is possible to write computer programs as long lists of numbers (machine language) and this technique was used with many early computers,[9] it is extremely tedious to do so in practice, especially for complicated programs. Instead, each basic instruction can be given a short name that is indicative of its function and easy to remember—a mnemonic such as ADD, SUB, MULT or JUMP. These mnemonics are collectively known as a computer's assembly language. Converting programs written in assembly language into something the computer can actually understand (machine language) is usually done by a computer program called an assembler. Machine languages and the assembly languages that represent them (collectively termed low-level programming languages) tend to be unique to a particular type of computer. For instance, an ARM architecture computer (such as may be found in a PDA or a hand-held videogame) cannot understand the machine language of an Intel Pentium or the AMD Athlon 64 computer that might be in a PC.[10]
Though considerably easier than in machine language, writing long programs in assembly language is often difficult and error prone. Therefore, most complicated programs are written in more abstract high-level programming languages that are able to express the needs of the computer programmer more conveniently (and thereby help reduce programmer error). High level languages are usually "compiled" into machine language (or sometimes into assembly language and then into machine language) using another computer program called a compiler.[11] Since high level languages are more abstract than assembly language, it is possible to use different compilers to translate the same high level language program into the machine language of many different types of computer. This is part of the means by which software like video games may be made available for different computer architectures such as personal computers and various video game consoles.
The task of developing large software systems is an immense intellectual effort. Producing software with an acceptably high reliability on a predictable schedule and budget has proved historically to be a great challenge; the academic and professional discipline of software engineering concentrates specifically on this problem.
Example
A traffic light showing red.
A traffic light showing red.
Suppose a computer is being employed to drive a traffic light. A simple stored program might say:
1. Turn off all of the lights
2. Turn on the red light
3. Wait for sixty seconds
4. Turn off the red light
5. Turn on the green light
6. Wait for sixty seconds
7. Turn off the green light
8. Turn on the yellow light
9. Wait for two seconds
10. Turn off the yellow light
11. Jump to instruction number (2)
With this set of instructions, the computer would cycle the light continually through red, green, yellow and back to red again until told to stop running the program.
However, suppose there is a simple on/off switch connected to the computer that is intended to be used to make the light flash red while some maintenance operation is being performed. The program might then instruct the computer to:
1. Turn off all of the lights
2. Turn on the red light
3. Wait for sixty seconds
4. Turn off the red light
5. Turn on the green light
6. Wait for sixty seconds
7. Turn off the green light
8. Turn on the yellow light
9. Wait for two seconds
10. Turn off the yellow light
11. If the maintenance switch is NOT turned on then jump to instruction number 2
12. Turn on the red light
13. Wait for one second
14. Turn off the red light
15. Wait for one second
16. Jump to instruction number 11
In this manner, the computer is either running the instructions from number (2) to (11) over and over or its running the instructions from (11) down to (16) over and over, depending on the position of the switch.[12]
How computers work
Main articles: Central processing unit and Microprocessor
A general purpose computer has four main sections: the arithmetic and logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by busses, often made of groups of wires.
The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these) are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.
Control unit
Main articles: CPU design and Control unit
The control unit (often called a control system or central controller) directs the various components of a computer. It reads and interprets (decodes) instructions in the program one by one. The control system decodes each instruction and turns it into a series of control signals that operate the other parts of the computer.[13] Control systems in advanced computers may change the order of some instructions so as to improve performance.
A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from.[14]
Diagram showing how a particular MIPS architecture instruction would be decoded by the control system.
Diagram showing how a particular MIPS architecture instruction would be decoded by the control system.
The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:
1. Read the code for the next instruction from the cell indicated by the program counter.
2. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
3. Increment the program counter so it points to the next instruction.
4. Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
5. Provide the necessary data to an ALU or register.
6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
7. Write the result from the ALU back to a memory location or to a register or perhaps an output device.
8. Jump back to step (1).
Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. Instructions that modify the program counter are often known as "jumps" and allow for loops (instructions that are repeated by the computer) and often conditional instruction execution (both examples of control flow).
It is noticeable that the sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program - and indeed, in some more complex CPU designs, there is another yet smaller computer called a microsequencer that runs a microcode program that causes all of these events to happen.
Arithmetic/logic unit (ALU)
This section does not cite any references or sources. (July 2008)
Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed.
Main article: Arithmetic logic unit
The ALU is capable of performing two classes of operations: arithmetic and logic.
The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc) and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers—albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?").
Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing boolean logic.
Superscalar computers contain multiple ALUs so that they can process several instructions at the same time. Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices.
Memory
Main article: Computer storage
Magnetic core memory was popular main memory for computers through the 1960s until it was completely replaced by semiconductor memory.
Magnetic core memory was popular main memory for computers through the 1960s until it was completely replaced by semiconductor memory.
A computer's memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered "address" and can store a single number. The computer can be instructed to "put the number 123 into the cell numbered 1357" or to "add the number that is in cell 1357 to the number that is in cell 2468 and put the answer into cell 1595". The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. Since the CPU does not differentiate between different types of information, it is up to the software to give significance to what the memory sees as nothing but a series of numbers.
In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers; either from 0 to 255 or -128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two's complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory as long as it can be somehow represented in numerical form. Modern computers have billions or even trillions of bytes of memory.
The CPU contains a special set of memory cells called registers that can be read and written to much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. Since data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer's speed.
Computer main memory comes in two principal varieties: random access memory or RAM and read-only memory or ROM. RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM is erased when the power to the computer is turned off while ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the software required to perform the task may be stored in ROM. Software that is stored in ROM is often called firmware because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM by retaining data when turned off but being rewritable like RAM. However, flash memory is typically much slower than conventional ROM and RAM so its use is restricted to applications where high speeds are not required.[15]
In more sophisticated computers there may be one or more RAM cache memories which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.
Input/output (I/O)
This section does not cite any references or sources. (July 2008)
Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed.
Main article: Input/output
Hard disks are common I/O devices used with computers.
Hard disks are common I/O devices used with computers.
I/O is the means by which a computer receives information from the outside world and sends results back. Devices that provide input or output to the computer are called peripherals. On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O.
Often, I/O devices are complex computers in their own right with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics[citation needed]. Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O.
Multitasking
This section does not cite any references or sources. (July 2008)
Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed.
Main article: Computer multitasking
While a computer may be viewed as running one gigantic program stored in its main memory, in some systems it is necessary to give the appearance of running several programs simultaneously. This is achieved by having the computer switch rapidly between running each program in turn. One means by which this is done is with a special signal called an interrupt which can periodically cause the computer to stop executing instructions where it was and do something else instead. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running "at the same time", then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time even though only one is ever executing in any given instant. This method of multitasking is sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn.
Before the era of cheap computers, the principle use for multitasking was to allow many people to share the same computer.
Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly - in direct proportion to the number of programs it is running. However, most programs spend much of their time waiting for slow input/output devices to complete their tasks. If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a "time slice" until the event it is waiting for has occurred. This frees up time for other programs to execute so that many programs may be run at the same time without unacceptable speed loss.
Multiprocessing
Main article: Multiprocessing
Cray designed many supercomputers that used multiprocessing heavily.
Cray designed many supercomputers that used multiprocessing heavily.
Some computers may divide their work between one or more separate CPUs, creating a multiprocessing configuration. Traditionally, this technique was utilized only in large and powerful computers such as supercomputers, mainframe computers and servers. However, multiprocessor and multi-core (multiple CPUs on a single integrated circuit) personal and laptop computers have become widely available and are beginning to see increased usage in lower-end markets as a result.
Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers.[16] They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful only for specialized tasks due to the large scale of program organization required to successfully utilize most of the available resources at once. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel" tasks.
Networking and the Internet
This section does not cite any references or sources. (July 2008)
Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed.
Main articles: Computer networking and Internet
Visualization of a portion of the routes on the Internet.
Visualization of a portion of the routes on the Internet.
Computers have been used to coordinate information between multiple locations since the 1950s. The U.S. military's SAGE system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems like Sabre.
In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. This effort was funded by ARPA (now DARPA), and the computer network that it produced was called the ARPANET. The technologies that made the Arpanet possible spread and evolved. In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become almost ubiquitous. In fact, the number of computers that are networked is growing phenomenally. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. "Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments.
Further topics
Hardware
Main article: Computer hardware
The term hardware covers all of those parts of a computer that are tangible objects. Circuits, displays, power supplies, cables, keyboards, printers and mice are all hardware.
History of computing hardware First Generation (Mechanical/Electromechanical) Calculators Antikythera mechanism, Difference Engine, Norden bombsight
Programmable Devices Jacquard loom, Analytical Engine, Harvard Mark I, Z3
Second Generation (Vacuum Tubes) Calculators Atanasoff–Berry Computer, IBM 604, UNIVAC 60, UNIVAC 120
Programmable Devices Colossus, ENIAC, Manchester Small-Scale Experimental Machine, EDSAC, Manchester Mark I, CSIRAC, EDVAC, UNIVAC I, IBM 701, IBM 702, IBM 650, Z22
Third Generation (Discrete transistors and SSI, MSI, LSI Integrated circuits) Mainframes IBM 7090, IBM 7080, System/360, BUNCH
Minicomputer PDP-8, PDP-11, System/32, System/36
Fourth Generation (VLSI integrated circuits) Minicomputer VAX, IBM System i
4-bit microcomputer Intel 4004, Intel 4040
8-bit microcomputer Intel 8008, Intel 8080, Motorola 6800, Motorola 6809, MOS Technology 6502, Zilog Z80
16-bit microcomputer Intel 8088, Zilog Z8000, WDC 65816/65802
32-bit microcomputer Intel 80386, Pentium, Motorola 68000, ARM architecture
64-bit microcomputer[17] x86-64, PowerPC, MIPS, SPARC
Embedded computer Intel 8048, Intel 8051
Personal computer Desktop computer, Home computer, Laptop computer, Personal digital assistant (PDA), Portable computer, Tablet computer, Wearable computer
Theoretical/experimental Quantum computer, Chemical computer, DNA computing, Optical computer, Spintronics based computer
Other Hardware Topics Peripheral device (Input/output) Input Mouse, Keyboard, Joystick, Image scanner
Output Monitor, Printer
Both Floppy disk drive, Hard disk, Optical disc drive, Teleprinter
Computer busses Short range RS-232, SCSI, PCI, USB
Long range (Computer networking) Ethernet, ATM, FDDI
Software
Main article: Computer software
Software refers to parts of the computer which do not have a material form, such as programs, data, protocols, etc. When software is stored in hardware that cannot easily be modified (such as BIOS ROM in an IBM PC compatible), it is sometimes called "firmware" to indicate that it falls into an uncertain area somewhere between hardware and software.
Computer software Operating system Unix/BSD UNIX System V, AIX, HP-UX, Solaris (SunOS), IRIX, List of BSD operating systems
GNU/Linux List of Linux distributions, Comparison of Linux distributions
Microsoft Windows Windows 95, Windows 98, Windows NT, Windows 2000, Windows XP, Windows Vista, Windows CE
DOS 86-DOS (QDOS), PC-DOS, MS-DOS, FreeDOS
Mac OS Mac OS classic, Mac OS X
Embedded and real-time List of embedded operating systems
Experimental Amoeba, Oberon/Bluebottle, Plan 9 from Bell Labs
Library Multimedia DirectX, OpenGL, OpenAL
Programming library C standard library, Standard template library
Data Protocol TCP/IP, Kermit, FTP, HTTP, SMTP
File format HTML, XML, JPEG, MPEG, PNG
User interface Graphical user interface (WIMP) Microsoft Windows, GNOME, KDE, QNX Photon, CDE, GEM
Text user interface Command line interface, shells
Application Office suite Word processing, Desktop publishing, Presentation program, Database management system, Scheduling & Time management, Spreadsheet, Accounting software
Internet Access Browser, E-mail client, Web server, Mail transfer agent, Instant messaging
Design and manufacturing Computer-aided design, Computer-aided manufacturing, Plant management, Robotic manufacturing, Supply chain management
Graphics Raster graphics editor, Vector graphics editor, 3D modeler, Animation editor, 3D computer graphics, Video editing, Image processing
Audio Digital audio editor, Audio playback, Mixing, Audio synthesis, Computer music
Software Engineering Compiler, Assembler, Interpreter, Debugger, Text Editor, Integrated development environment, Performance analysis, Revision control, Software configuration management
Educational Edutainment, Educational game, Serious game, Flight simulator
Games Strategy, Arcade, Puzzle, Simulation, First-person shooter, Platform, Massively multiplayer, Interactive fiction
Misc Artificial intelligence, Antivirus software, Malware scanner, Installer/Package management systems, File manager
Programming languages
Programming languages provide various ways of specifying programs for computers to run. Unlike natural languages, programming languages are designed to permit no ambiguity and to be concise. They are purely written languages and are often difficult to read aloud. They are generally either translated into machine language by a compiler or an assembler before being run, or translated directly at run time by an interpreter. Sometimes programs are executed by a hybrid method of the two techniques. There are thousands of different programming languages—some intended to be general purpose, others useful only for highly specialized applications.
Programming Languages Lists of programming languages Timeline of programming languages, Categorical list of programming languages, Generational list of programming languages, Alphabetical list of programming languages, Non-English-based programming languages
Commonly used Assembly languages ARM, MIPS, x86
Commonly used High level languages BASIC, C, C++, C#, COBOL, Fortran, Java, Lisp, Pascal
Commonly used Scripting languages Bourne script, JavaScript, Python, Ruby, PHP, Perl
Professions and organizations
As the use of computers has spread throughout society, there are an increasing number of careers involving computers. Following the theme of hardware, software and firmware, the brains of people who work in the industry are sometimes known irreverently as wetware or "meatware".
Computer-related professions Hardware-related Electrical engineering, Electronics engineering, Computer engineering, Telecommunications engineering, Optical engineering, Nanoscale engineering
Software-related Computer science, Human-computer interaction, Information technology, Software engineering, Scientific computing, Web design, Desktop publishing
The need for computers to work well together and to be able to exchange information has spawned the need for many standards organizations, clubs and societies of both a formal and informal nature.
Organizations Standards groups ANSI, IEC, IEEE, IETF, ISO, W3C
Professional Societies ACM, ACM Special Interest Groups, IET, IFIP
Free/Open source software groups Free Software Foundation, Mozilla Foundation, Apache Software Foundation
See also
Look up Computer in
Wiktionary, the free dictionary.
Wikiquote has a collection of quotations related to:
Computers
Wikimedia Commons has media related to:
Computer
* Computability theory
* Computer science
* Computing
* Computers in fiction
* Computer security and Computer insecurity
* Electronic waste
* List of computer term etymologies
* Virtualization
Notes
1. ^ In 1946, ENIAC consumed an estimated 174 kW. By comparison, a typical personal computer may use around 400 W; over four hundred times less. (Kempf 1961)
2. ^ Early computers such as Colossus and ENIAC were able to process between 5 and 100 operations per second. A modern "commodity" microprocessor (as of 2007) can process billions of operations per second, and many of these operations are more complicated and useful than early computer operations.
3. ^ "Heron of Alexandria". Retrieved on 2008-01-15.
4. ^ The Analytical Engine should not be confused with Babbage's difference engine which was a non-programmable mechanical calculator.
5. ^ B. Jack Copeland, ed., Colossus: The Secrets of Bletchley Park's Codebreaking Computers, Oxford University Press, 2006
6. ^ This program was written similarly to those for the PDP-11 minicomputer and shows some typical things a computer can do. All the text after the semicolons are comments for the benefit of human readers. These have no significance to the computer and are ignored. (Digital Equipment Corporation 1972)
7. ^ Attempts are often made to create programs that can overcome this fundamental limitation of computers. Software that mimics learning and adaptation is part of artificial intelligence.
8. ^ It is not universally true that bugs are solely due to programmer oversight. Computer hardware may fail or may itself have a fundamental problem that produces unexpected results in certain situations. For instance, the Pentium FDIV bug caused some Intel microprocessors in the early 1990s to produce inaccurate results for certain floating point division operations. This was caused by a flaw in the microprocessor design and resulted in a partial recall of the affected devices.
9. ^ Even some later computers were commonly programmed directly in machine code. Some minicomputers like the DEC PDP-8 could be programmed directly from a panel of switches. However, this method was usually used only as part of the booting process. Most modern computers boot entirely automatically by reading a boot program from some non-volatile memory.
10. ^ However, there is sometimes some form of machine language compatibility between different computers. An x86-64 compatible microprocessor like the AMD Athlon 64 is able to run most of the same programs that an Intel Core 2 microprocessor can, as well as programs designed for earlier microprocessors like the Intel Pentiums and Intel 80486. This contrasts with very early commercial computers, which were often one-of-a-kind and totally incompatible with other computers.
11. ^ High level languages are also often interpreted rather than compiled. Interpreted languages are translated into machine code on the fly by another program called an interpreter.
12. ^ Although this is a simple program, it contains a software bug. If the traffic signal is showing red when someone switches the "flash red" switch, it will cycle through green once more before starting to flash red as instructed. This bug is quite easy to fix by changing the program to repeatedly test the switch throughout each "wait" period—but writing large programs that have no bugs is exceedingly difficult.
13. ^ The control unit's rule in interpreting instructions has varied somewhat in the past. While the control unit is solely responsible for instruction interpretation in most modern computers, this is not always the case. Many computers include some instructions that may only be partially interpreted by the control system and partially interpreted by another device. This is especially the case with specialized computing hardware that may be partially self-contained. For example, EDVAC, the first modern stored program computer to be designed, used a central control unit that only interpreted four instructions. All of the arithmetic-related instructions were passed on to its arithmetic unit and further decoded there.
14. ^ Instructions often occupy more than one memory address, so the program counters usually increases by the number of memory locations required to store one instruction.
15. ^ Flash memory also may only be rewritten a limited number of times before wearing out, making it less useful for heavy random access usage. (Verma 1988)
16. ^ However, it is also very common to construct supercomputers out of many pieces of cheap commodity hardware; usually individual computers connected by networks. These so-called computer clusters can often provide supercomputer performance at a much lower cost than customized designs. While custom architectures are still used for most of the most powerful supercomputers, there has been a proliferation of cluster computers in recent years. (TOP500 2006)
17. ^ Most major 64-bit instruction set architectures are extensions of earlier designs. All of the architectures listed in this table existed in 32-bit forms before their 64-bit incarnations were introduced.
References
* a Kempf, Karl (1961). "Historical Monograph: Electronic Computers Within the Ordnance Corps". Aberdeen Proving Ground (United States Army).
* a Phillips, Tony (2000). "The Antikythera Mechanism I". American Mathematical Society. Retrieved on 2006-04-05.
* a Shannon, Claude Elwood (1940). "A symbolic analysis of relay and switching circuits". Massachusetts Institute of Technology.
* a Digital Equipment Corporation (1972). PDP-11/40 Processor Handbook (PDF), Maynard, MA: Digital Equipment Corporation.
* a Verma, G.; Mielke, N. (1988). "Reliability performance of ETOX based flash memories". IEEE International Reliability Physics Symposium.
* a Meuer, Hans; Strohmaier, Erich; Simon, Horst; Dongarra, Jack (2006-11-13). "Architectures Share Over Time". TOP500. Retrieved on 2006-11-27.
* Stokes, Jon (2007). Inside the Machine: An Illustrated Introduction to Microprocessors and Computer Architecture. San Francisco: No Starch Press. ISBN 978-1-59327-104-6.
Retrieved from "http://en.wikipedia.org/wiki/Computer"
Categories: Computing
Hidden categories: Semi-protected | Articles needing additional references from July 2008 | All articles with unsourced statements | Articles with unsourced statements since December 2007
Views
* Article
* Discussion
* View source
* History
Personal tools
* Log in / create account
Navigation
* Main Page
* Contents
* Featured content
* Current events
* Random article
Search
Interaction
* About Wikipedia
* Community portal
* Recent changes
* Contact Wikipedia
* Donate to Wikipedia
* Help
Toolbox
* What links here
* Related changes
* Upload file
* Special pages
* Printable version
* Permanent link
* Cite this page
Languages
* Afrikaans
* አማርኛ
* Anglo-Saxon
* العربية
* Aragonés
* Asturianu
* Azərbaycan
* বাংলা
* Bân-lâm-gú
* Башҡорт
* Беларуская (тарашкевіца)
* Boarisch
* Bosanski
* Brezhoneg
* Български
* Català
* Чăвашла
* Česky
* Cymraeg
* Dansk
* Deutsch
* Diné bizaad
* Eesti
* Ελληνικά
* Español
* Esperanto
* Euskara
* فارسی
* Føroyskt
* Français
* Frysk
* Furlan
* Gaeilge
* Gàidhlig
* Galego
* ������������
* 한국어
* Հայերեն
* हिन्दी
* Hrvatski
* Ido
* ইমার ঠার/বিষ্ণুপ্রিয়া মণিপুরী
* Bahasa Indonesia
* Interlingua
* ᐃᓄᒃᑎᑐᑦ/inuktitut
* isiZulu
* Íslenska
* Italiano
* עברית
* Basa Jawa
* ಕನ್ನಡ
* ქართული
* Қазақша
* Kernewek
* Kiswahili
* Kongo
* Kurdî / كوردی
* ລາວ
* Latina
* Latviešu
* Lëtzebuergesch
* Lietuvių
* Limburgs
* Lingála
* Magyar
* Македонски
* Malagasy
* മലയാളം
* Malti
* मराठी
* Bahasa Melayu
* Монгол
* Myanmasa
* Nahuatl
* Nederlands
* Nedersaksisch
* नेपाली
* नेपाल भाषा
* 日本語
* Nnapulitano
* Norsk (bokmål)
* Norsk (nynorsk)
* Occitan
* O'zbek
* ਪੰਜਾਬੀ
* Plattdüütsch
* Polski
* Português
* Română
* Runa Simi
* Русский
* Scots
* Shqip
* Sicilianu
* සිංහල
* Simple English
* Slovenčina
* Словѣ́ньскъ / ⰔⰎⰑⰂⰡⰐⰠⰔⰍⰟ
* Slovenščina
* Soomaaliga
* Српски / Srpski
* Srpskohrvatski / Српскохрватски
* Basa Sunda
* Suomi
* Svenska
* Tagalog
* தமிழ்
* తెలుగు
* ไทย
* Tiếng Việt
* Тоҷикӣ/tojikī
* Türkçe
* Українська
* اردو
* Vèneto
* Walon
* Wolof
* ייִדיש
* 粵語
* Zazaki
* Žemaitėška
* 中文
Powered by MediaWiki
Wikimedia Foundation
The first devices that resemble modern computers date to the mid-20th century (around 1940 - 1945), although the computer concept and various machines similar to computers existed earlier. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers.[1] Modern computers are based on tiny integrated circuits and are millions to billions of times more capable while occupying a fraction of the space.[2] Today, simple computers may be made small enough to fit into a wristwatch and be powered from a watch battery. Personal computers, in various forms, are icons of the Information Age and are what most people think of as "a computer"; however, the most common form of computer in use today is the embedded computer. Embedded computers are small, simple devices that are used to control other devices — for example, they may be found in machines ranging from fighter aircraft to industrial robots, digital cameras, and children's toys.
The ability to store and execute lists of instructions called programs makes computers extremely versatile and distinguishes them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, computers with capability and complexity ranging from that of a personal digital assistant to a supercomputer are all able to perform the same computational tasks given enough time and storage capacity.
Contents
[hide]
* 1 History of computing
* 2 Stored program architecture
o 2.1 Programs
o 2.2 Example
* 3 How computers work
o 3.1 Control unit
o 3.2 Arithmetic/logic unit (ALU)
o 3.3 Memory
o 3.4 Input/output (I/O)
o 3.5 Multitasking
o 3.6 Multiprocessing
o 3.7 Networking and the Internet
* 4 Further topics
o 4.1 Hardware
o 4.2 Software
o 4.3 Programming languages
o 4.4 Professions and organizations
* 5 See also
* 6 Notes
* 7 References
History of computing
Main article: History of computer hardware
The Jacquard loom was one of the first programmable devices.
The Jacquard loom was one of the first programmable devices.
It is difficult to identify any one device as the earliest computer, partly because the term "computer" has been subject to varying interpretations over time. Originally, the term "computer" referred to a person who performed numerical calculations (a human computer), often with the aid of a mechanical calculating device.
The history of the modern computer begins with two separate technologies - that of automated calculation and that of programmability.
Examples of early mechanical calculating devices included the abacus, the slide rule and arguably the astrolabe and the Antikythera mechanism (which dates from about 150-100 BC). The end of the Middle Ages saw a re-invigoration of European mathematics and engineering, and Wilhelm Schickard's 1623 device was the first of a number of mechanical calculators constructed by European engineers. However, none of those devices fit the modern definition of a computer because they could not be programmed.
Hero of Alexandria (c. 10 – 70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions - and when.[3] This is the essence of programmability. In 1801, Joseph Marie Jacquard made an improvement to the textile loom that used a series of punched paper cards as a template to allow his loom to weave intricate patterns automatically. The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven patterns can be viewed as an early, albeit limited, form of programmability.
It was the fusion of automatic calculation with programmability that produced the first recognizable computers. In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer that he called "The Analytical Engine".[4] Due to limited finances, and an inability to resist tinkering with the design, Babbage never actually built his Analytical Engine.
Large-scale automated data processing of punched cards was performed for the U.S. Census in 1890 by tabulating machines designed by Herman Hollerith and manufactured by the Computing Tabulating Recording Corporation, which later became IBM. By the end of the 19th century a number of technologies that would later prove useful in the realization of practical computers had begun to appear: the punched card, Boolean algebra, the vacuum tube (thermionic valve) and the teleprinter.
During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.
Defining characteristics of some early digital computers of the 1940s (In the history of computing hardware) Name First operational Numeral system Computing mechanism Programming Turing complete
Zuse Z3 (Germany) May 1941 Binary Electro-mechanical Program-controlled by punched film stock Yes (1998)
Atanasoff–Berry Computer (USA) Summer 1941 Binary Electronic Not programmable—single purpose No
Colossus (UK) January 1944 Binary Electronic Program-controlled by patch cables and switches No
Harvard Mark I – IBM ASCC (USA) 1944 Decimal Electro-mechanical Program-controlled by 24-channel punched paper tape (but no conditional branch) Yes (1998)
ENIAC (USA) November 1945 Decimal Electronic Program-controlled by patch cables and switches Yes
Manchester Small-Scale Experimental Machine (UK) June 1948 Binary Electronic Stored-program in Williams cathode ray tube memory Yes
Modified ENIAC (USA) September 1948 Decimal Electronic Program-controlled by patch cables and switches plus a primitive read-only stored programming mechanism using the Function Tables as program ROM Yes
EDSAC (UK) May 1949 Binary Electronic Stored-program in mercury delay line memory Yes
Manchester Mark I (UK) October 1949 Binary Electronic Stored-program in Williams cathode ray tube memory and magnetic drum memory Yes
CSIRAC (Australia) November 1949 Binary Electronic Stored-program in mercury delay line memory Yes
A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features that are seen in modern computers. The use of digital electronics (largely invented by Claude Shannon in 1937) and more flexible programmability were vitally important steps, but defining one point along this road as "the first digital electronic computer" is difficult (Shannon 1940). Notable achievements include:
EDSAC was one of the first computers to implement the stored program (von Neumann) architecture.
EDSAC was one of the first computers to implement the stored program (von Neumann) architecture.
* Konrad Zuse's electromechanical "Z machines". The Z3 (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability. In 1998 the Z3 was proved to be Turing complete, therefore being the world's first operational computer.
* The non-programmable Atanasoff–Berry Computer (1941) which used vacuum tube based computation, binary numbers, and regenerative capacitor memory.
* The secret British Colossus computers (1943)[5], which had limited programmability but demonstrated that a device using thousands of tubes could be reasonably reliable and electronically reprogrammable. It was used for breaking German wartime codes.
* The Harvard Mark I (1944), a large-scale electromechanical computer with limited programmability.
* The U.S. Army's Ballistics Research Laboratory ENIAC (1946), which used decimal arithmetic and is sometimes called the first general purpose electronic computer (since Konrad Zuse's Z3 of 1941 used electromagnets instead of electronics). Initially, however, ENIAC had an inflexible architecture which essentially required rewiring to change its programming.
Several developers of ENIAC, recognizing its flaws, came up with a far more flexible and elegant design, which came to be known as the "stored program architecture" or von Neumann architecture. This design was first formally described by John von Neumann in the paper First Draft of a Report on the EDVAC, distributed in 1945. A number of projects to develop computers based on the stored-program architecture commenced around this time, the first of these being completed in Great Britain. The first to be demonstrated working was the Manchester Small-Scale Experimental Machine (SSEM or "Baby"), while the EDSAC, completed a year after SSEM, was the first practical implementation of the stored program design. Shortly thereafter, the machine originally described by von Neumann's paper—EDVAC—was completed but did not see full-time use for an additional two years.
Nearly all modern computers implement some form of the stored-program architecture, making it the single trait by which the word "computer" is now defined. While the technologies used in computers have changed dramatically since the first electronic, general-purpose computers of the 1940s, most still use the von Neumann architecture.
Microprocessors are miniaturized devices that often implement stored program CPUs.
Microprocessors are miniaturized devices that often implement stored program CPUs.
Computers that used vacuum tubess as their electronic elements were in use throughout the 1950s. Vacuum tube electronics were largely replaced in the 1960s by transistor-based electronics, which are smaller, faster, cheaper to produce, require less power, and are more reliable. In the 1970s, integrated circuit technology and the subsequent creation of microprocessors, such as the Intel 4004, further decreased size and cost and further increased speed and reliability of computers. By the 1980s, computers became sufficiently small and cheap to replace simple mechanical controls in domestic appliances such as washing machines. The 1980s also witnessed home computers and the now ubiquitous personal computer. With the evolution of the Internet, personal computers are becoming as common as the television and the telephone in the household.
Stored program architecture
Main articles: Computer program and Computer programming
The defining feature of modern computers which distinguishes them from all other machines is that they can be programmed. That is to say that a list of instructions (the program) can be given to the computer and it will store them and carry them out at some time in the future.
In most cases, computer instructions are simple: add one number to another, move some data from one location to another, send a message to some external device, etc. These instructions are read from the computer's memory and are generally carried out (executed) in the order they were given. However, there are usually specialized instructions to tell the computer to jump ahead or backwards to some other place in the program and to carry on executing from there. These are called "jump" instructions (or branches). Furthermore, jump instructions may be made to happen conditionally so that different sequences of instructions may be used depending on the result of some previous calculation or some external event. Many computers directly support subroutines by providing a type of jump that "remembers" the location it jumped from and another instruction to return to the instruction following that jump instruction.
Program execution might be likened to reading a book. While a person will normally read each word and line in sequence, they may at times jump back to an earlier place in the text or skip sections that are not of interest. Similarly, a computer may sometimes go back and repeat the instructions in some section of the program over and over again until some internal condition is met. This is called the flow of control within the program and it is what allows the computer to perform tasks repeatedly without human intervention.
Comparatively, a person using a pocket calculator can perform a basic arithmetic operation such as adding two numbers with just a few button presses. But to add together all of the numbers from 1 to 1,000 would take thousands of button presses and a lot of time—with a near certainty of making a mistake. On the other hand, a computer may be programmed to do this with just a few simple instructions. For example:
mov #0,sum ; set sum to 0
mov #1,num ; set num to 1
loop: add num,sum ; add num to sum
add #1,num ; add 1 to num
cmp num,#1000 ; compare num to 1000
ble loop ; if num <= 1000, go back to 'loop'
halt ; end of program. stop running
Once told to run this program, the computer will perform the repetitive addition task without further human intervention. It will almost never make a mistake and a modern PC can complete the task in about a millionth of a second.[6]
However, computers cannot "think" for themselves in the sense that they only solve problems in exactly the way they are programmed to. An intelligent human faced with the above addition task might soon realize that instead of actually adding up all the numbers one can simply use the equation
1+2+3+...+n = {{n(n+1)} \over 2}
and arrive at the correct answer (500,500) with little work.[7] In other words, a computer programmed to add up the numbers one by one as in the example above would do exactly that without regard to efficiency or alternative solutions.
Programs
A 1970s punched card containing one line from a FORTRAN program. The card reads: "Z(1) = Y + W(1)" and is labelled "PROJ039" for identification purposes.
A 1970s punched card containing one line from a FORTRAN program. The card reads: "Z(1) = Y + W(1)" and is labelled "PROJ039" for identification purposes.
In practical terms, a computer program may run from just a few instructions to many millions of instructions, as in a program for a word processor or a web browser. A typical modern computer can execute billions of instructions per second (gigahertz or GHz) and rarely make a mistake over many years of operation. Large computer programs comprising several million instructions may take teams of programmers years to write, thus the probability of the entire program having been written without error is highly unlikely.
Errors in computer programs are called "bugs". Bugs may be benign and not affect the usefulness of the program, or have only subtle effects. But in some cases they may cause the program to "hang" - become unresponsive to input such as mouse clicks or keystrokes, or to completely fail or "crash". Otherwise benign bugs may sometimes may be harnessed for malicious intent by an unscrupulous user writing an "exploit" - code designed to take advantage of a bug and disrupt a program's proper execution. Bugs are usually not the fault of the computer. Since computers merely execute the instructions they are given, bugs are nearly always the result of programmer error or an oversight made in the program's design.[8]
In most computers, individual instructions are stored as machine code with each instruction being given a unique number (its operation code or opcode for short). The command to add two numbers together would have one opcode, the command to multiply them would have a different opcode and so on. The simplest computers are able to perform any of a handful of different instructions; the more complex computers have several hundred to choose from—each with a unique numerical code. Since the computer's memory is able to store numbers, it can also store the instruction codes. This leads to the important fact that entire programs (which are just lists of instructions) can be represented as lists of numbers and can themselves be manipulated inside the computer just as if they were numeric data. The fundamental concept of storing programs in the computer's memory alongside the data they operate on is the crux of the von Neumann, or stored program, architecture. In some cases, a computer might store some or all of its program in memory that is kept separate from the data it operates on. This is called the Harvard architecture after the Harvard Mark I computer. Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in CPU caches.
While it is possible to write computer programs as long lists of numbers (machine language) and this technique was used with many early computers,[9] it is extremely tedious to do so in practice, especially for complicated programs. Instead, each basic instruction can be given a short name that is indicative of its function and easy to remember—a mnemonic such as ADD, SUB, MULT or JUMP. These mnemonics are collectively known as a computer's assembly language. Converting programs written in assembly language into something the computer can actually understand (machine language) is usually done by a computer program called an assembler. Machine languages and the assembly languages that represent them (collectively termed low-level programming languages) tend to be unique to a particular type of computer. For instance, an ARM architecture computer (such as may be found in a PDA or a hand-held videogame) cannot understand the machine language of an Intel Pentium or the AMD Athlon 64 computer that might be in a PC.[10]
Though considerably easier than in machine language, writing long programs in assembly language is often difficult and error prone. Therefore, most complicated programs are written in more abstract high-level programming languages that are able to express the needs of the computer programmer more conveniently (and thereby help reduce programmer error). High level languages are usually "compiled" into machine language (or sometimes into assembly language and then into machine language) using another computer program called a compiler.[11] Since high level languages are more abstract than assembly language, it is possible to use different compilers to translate the same high level language program into the machine language of many different types of computer. This is part of the means by which software like video games may be made available for different computer architectures such as personal computers and various video game consoles.
The task of developing large software systems is an immense intellectual effort. Producing software with an acceptably high reliability on a predictable schedule and budget has proved historically to be a great challenge; the academic and professional discipline of software engineering concentrates specifically on this problem.
Example
A traffic light showing red.
A traffic light showing red.
Suppose a computer is being employed to drive a traffic light. A simple stored program might say:
1. Turn off all of the lights
2. Turn on the red light
3. Wait for sixty seconds
4. Turn off the red light
5. Turn on the green light
6. Wait for sixty seconds
7. Turn off the green light
8. Turn on the yellow light
9. Wait for two seconds
10. Turn off the yellow light
11. Jump to instruction number (2)
With this set of instructions, the computer would cycle the light continually through red, green, yellow and back to red again until told to stop running the program.
However, suppose there is a simple on/off switch connected to the computer that is intended to be used to make the light flash red while some maintenance operation is being performed. The program might then instruct the computer to:
1. Turn off all of the lights
2. Turn on the red light
3. Wait for sixty seconds
4. Turn off the red light
5. Turn on the green light
6. Wait for sixty seconds
7. Turn off the green light
8. Turn on the yellow light
9. Wait for two seconds
10. Turn off the yellow light
11. If the maintenance switch is NOT turned on then jump to instruction number 2
12. Turn on the red light
13. Wait for one second
14. Turn off the red light
15. Wait for one second
16. Jump to instruction number 11
In this manner, the computer is either running the instructions from number (2) to (11) over and over or its running the instructions from (11) down to (16) over and over, depending on the position of the switch.[12]
How computers work
Main articles: Central processing unit and Microprocessor
A general purpose computer has four main sections: the arithmetic and logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by busses, often made of groups of wires.
The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these) are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.
Control unit
Main articles: CPU design and Control unit
The control unit (often called a control system or central controller) directs the various components of a computer. It reads and interprets (decodes) instructions in the program one by one. The control system decodes each instruction and turns it into a series of control signals that operate the other parts of the computer.[13] Control systems in advanced computers may change the order of some instructions so as to improve performance.
A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from.[14]
Diagram showing how a particular MIPS architecture instruction would be decoded by the control system.
Diagram showing how a particular MIPS architecture instruction would be decoded by the control system.
The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:
1. Read the code for the next instruction from the cell indicated by the program counter.
2. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
3. Increment the program counter so it points to the next instruction.
4. Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
5. Provide the necessary data to an ALU or register.
6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
7. Write the result from the ALU back to a memory location or to a register or perhaps an output device.
8. Jump back to step (1).
Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. Instructions that modify the program counter are often known as "jumps" and allow for loops (instructions that are repeated by the computer) and often conditional instruction execution (both examples of control flow).
It is noticeable that the sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program - and indeed, in some more complex CPU designs, there is another yet smaller computer called a microsequencer that runs a microcode program that causes all of these events to happen.
Arithmetic/logic unit (ALU)
This section does not cite any references or sources. (July 2008)
Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed.
Main article: Arithmetic logic unit
The ALU is capable of performing two classes of operations: arithmetic and logic.
The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc) and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers—albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?").
Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing boolean logic.
Superscalar computers contain multiple ALUs so that they can process several instructions at the same time. Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices.
Memory
Main article: Computer storage
Magnetic core memory was popular main memory for computers through the 1960s until it was completely replaced by semiconductor memory.
Magnetic core memory was popular main memory for computers through the 1960s until it was completely replaced by semiconductor memory.
A computer's memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered "address" and can store a single number. The computer can be instructed to "put the number 123 into the cell numbered 1357" or to "add the number that is in cell 1357 to the number that is in cell 2468 and put the answer into cell 1595". The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. Since the CPU does not differentiate between different types of information, it is up to the software to give significance to what the memory sees as nothing but a series of numbers.
In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers; either from 0 to 255 or -128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two's complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory as long as it can be somehow represented in numerical form. Modern computers have billions or even trillions of bytes of memory.
The CPU contains a special set of memory cells called registers that can be read and written to much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. Since data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer's speed.
Computer main memory comes in two principal varieties: random access memory or RAM and read-only memory or ROM. RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM is erased when the power to the computer is turned off while ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the software required to perform the task may be stored in ROM. Software that is stored in ROM is often called firmware because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM by retaining data when turned off but being rewritable like RAM. However, flash memory is typically much slower than conventional ROM and RAM so its use is restricted to applications where high speeds are not required.[15]
In more sophisticated computers there may be one or more RAM cache memories which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.
Input/output (I/O)
This section does not cite any references or sources. (July 2008)
Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed.
Main article: Input/output
Hard disks are common I/O devices used with computers.
Hard disks are common I/O devices used with computers.
I/O is the means by which a computer receives information from the outside world and sends results back. Devices that provide input or output to the computer are called peripherals. On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O.
Often, I/O devices are complex computers in their own right with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics[citation needed]. Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O.
Multitasking
This section does not cite any references or sources. (July 2008)
Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed.
Main article: Computer multitasking
While a computer may be viewed as running one gigantic program stored in its main memory, in some systems it is necessary to give the appearance of running several programs simultaneously. This is achieved by having the computer switch rapidly between running each program in turn. One means by which this is done is with a special signal called an interrupt which can periodically cause the computer to stop executing instructions where it was and do something else instead. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running "at the same time", then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time even though only one is ever executing in any given instant. This method of multitasking is sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn.
Before the era of cheap computers, the principle use for multitasking was to allow many people to share the same computer.
Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly - in direct proportion to the number of programs it is running. However, most programs spend much of their time waiting for slow input/output devices to complete their tasks. If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a "time slice" until the event it is waiting for has occurred. This frees up time for other programs to execute so that many programs may be run at the same time without unacceptable speed loss.
Multiprocessing
Main article: Multiprocessing
Cray designed many supercomputers that used multiprocessing heavily.
Cray designed many supercomputers that used multiprocessing heavily.
Some computers may divide their work between one or more separate CPUs, creating a multiprocessing configuration. Traditionally, this technique was utilized only in large and powerful computers such as supercomputers, mainframe computers and servers. However, multiprocessor and multi-core (multiple CPUs on a single integrated circuit) personal and laptop computers have become widely available and are beginning to see increased usage in lower-end markets as a result.
Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers.[16] They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful only for specialized tasks due to the large scale of program organization required to successfully utilize most of the available resources at once. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel" tasks.
Networking and the Internet
This section does not cite any references or sources. (July 2008)
Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed.
Main articles: Computer networking and Internet
Visualization of a portion of the routes on the Internet.
Visualization of a portion of the routes on the Internet.
Computers have been used to coordinate information between multiple locations since the 1950s. The U.S. military's SAGE system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems like Sabre.
In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. This effort was funded by ARPA (now DARPA), and the computer network that it produced was called the ARPANET. The technologies that made the Arpanet possible spread and evolved. In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become almost ubiquitous. In fact, the number of computers that are networked is growing phenomenally. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. "Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments.
Further topics
Hardware
Main article: Computer hardware
The term hardware covers all of those parts of a computer that are tangible objects. Circuits, displays, power supplies, cables, keyboards, printers and mice are all hardware.
History of computing hardware First Generation (Mechanical/Electromechanical) Calculators Antikythera mechanism, Difference Engine, Norden bombsight
Programmable Devices Jacquard loom, Analytical Engine, Harvard Mark I, Z3
Second Generation (Vacuum Tubes) Calculators Atanasoff–Berry Computer, IBM 604, UNIVAC 60, UNIVAC 120
Programmable Devices Colossus, ENIAC, Manchester Small-Scale Experimental Machine, EDSAC, Manchester Mark I, CSIRAC, EDVAC, UNIVAC I, IBM 701, IBM 702, IBM 650, Z22
Third Generation (Discrete transistors and SSI, MSI, LSI Integrated circuits) Mainframes IBM 7090, IBM 7080, System/360, BUNCH
Minicomputer PDP-8, PDP-11, System/32, System/36
Fourth Generation (VLSI integrated circuits) Minicomputer VAX, IBM System i
4-bit microcomputer Intel 4004, Intel 4040
8-bit microcomputer Intel 8008, Intel 8080, Motorola 6800, Motorola 6809, MOS Technology 6502, Zilog Z80
16-bit microcomputer Intel 8088, Zilog Z8000, WDC 65816/65802
32-bit microcomputer Intel 80386, Pentium, Motorola 68000, ARM architecture
64-bit microcomputer[17] x86-64, PowerPC, MIPS, SPARC
Embedded computer Intel 8048, Intel 8051
Personal computer Desktop computer, Home computer, Laptop computer, Personal digital assistant (PDA), Portable computer, Tablet computer, Wearable computer
Theoretical/experimental Quantum computer, Chemical computer, DNA computing, Optical computer, Spintronics based computer
Other Hardware Topics Peripheral device (Input/output) Input Mouse, Keyboard, Joystick, Image scanner
Output Monitor, Printer
Both Floppy disk drive, Hard disk, Optical disc drive, Teleprinter
Computer busses Short range RS-232, SCSI, PCI, USB
Long range (Computer networking) Ethernet, ATM, FDDI
Software
Main article: Computer software
Software refers to parts of the computer which do not have a material form, such as programs, data, protocols, etc. When software is stored in hardware that cannot easily be modified (such as BIOS ROM in an IBM PC compatible), it is sometimes called "firmware" to indicate that it falls into an uncertain area somewhere between hardware and software.
Computer software Operating system Unix/BSD UNIX System V, AIX, HP-UX, Solaris (SunOS), IRIX, List of BSD operating systems
GNU/Linux List of Linux distributions, Comparison of Linux distributions
Microsoft Windows Windows 95, Windows 98, Windows NT, Windows 2000, Windows XP, Windows Vista, Windows CE
DOS 86-DOS (QDOS), PC-DOS, MS-DOS, FreeDOS
Mac OS Mac OS classic, Mac OS X
Embedded and real-time List of embedded operating systems
Experimental Amoeba, Oberon/Bluebottle, Plan 9 from Bell Labs
Library Multimedia DirectX, OpenGL, OpenAL
Programming library C standard library, Standard template library
Data Protocol TCP/IP, Kermit, FTP, HTTP, SMTP
File format HTML, XML, JPEG, MPEG, PNG
User interface Graphical user interface (WIMP) Microsoft Windows, GNOME, KDE, QNX Photon, CDE, GEM
Text user interface Command line interface, shells
Application Office suite Word processing, Desktop publishing, Presentation program, Database management system, Scheduling & Time management, Spreadsheet, Accounting software
Internet Access Browser, E-mail client, Web server, Mail transfer agent, Instant messaging
Design and manufacturing Computer-aided design, Computer-aided manufacturing, Plant management, Robotic manufacturing, Supply chain management
Graphics Raster graphics editor, Vector graphics editor, 3D modeler, Animation editor, 3D computer graphics, Video editing, Image processing
Audio Digital audio editor, Audio playback, Mixing, Audio synthesis, Computer music
Software Engineering Compiler, Assembler, Interpreter, Debugger, Text Editor, Integrated development environment, Performance analysis, Revision control, Software configuration management
Educational Edutainment, Educational game, Serious game, Flight simulator
Games Strategy, Arcade, Puzzle, Simulation, First-person shooter, Platform, Massively multiplayer, Interactive fiction
Misc Artificial intelligence, Antivirus software, Malware scanner, Installer/Package management systems, File manager
Programming languages
Programming languages provide various ways of specifying programs for computers to run. Unlike natural languages, programming languages are designed to permit no ambiguity and to be concise. They are purely written languages and are often difficult to read aloud. They are generally either translated into machine language by a compiler or an assembler before being run, or translated directly at run time by an interpreter. Sometimes programs are executed by a hybrid method of the two techniques. There are thousands of different programming languages—some intended to be general purpose, others useful only for highly specialized applications.
Programming Languages Lists of programming languages Timeline of programming languages, Categorical list of programming languages, Generational list of programming languages, Alphabetical list of programming languages, Non-English-based programming languages
Commonly used Assembly languages ARM, MIPS, x86
Commonly used High level languages BASIC, C, C++, C#, COBOL, Fortran, Java, Lisp, Pascal
Commonly used Scripting languages Bourne script, JavaScript, Python, Ruby, PHP, Perl
Professions and organizations
As the use of computers has spread throughout society, there are an increasing number of careers involving computers. Following the theme of hardware, software and firmware, the brains of people who work in the industry are sometimes known irreverently as wetware or "meatware".
Computer-related professions Hardware-related Electrical engineering, Electronics engineering, Computer engineering, Telecommunications engineering, Optical engineering, Nanoscale engineering
Software-related Computer science, Human-computer interaction, Information technology, Software engineering, Scientific computing, Web design, Desktop publishing
The need for computers to work well together and to be able to exchange information has spawned the need for many standards organizations, clubs and societies of both a formal and informal nature.
Organizations Standards groups ANSI, IEC, IEEE, IETF, ISO, W3C
Professional Societies ACM, ACM Special Interest Groups, IET, IFIP
Free/Open source software groups Free Software Foundation, Mozilla Foundation, Apache Software Foundation
See also
Look up Computer in
Wiktionary, the free dictionary.
Wikiquote has a collection of quotations related to:
Computers
Wikimedia Commons has media related to:
Computer
* Computability theory
* Computer science
* Computing
* Computers in fiction
* Computer security and Computer insecurity
* Electronic waste
* List of computer term etymologies
* Virtualization
Notes
1. ^ In 1946, ENIAC consumed an estimated 174 kW. By comparison, a typical personal computer may use around 400 W; over four hundred times less. (Kempf 1961)
2. ^ Early computers such as Colossus and ENIAC were able to process between 5 and 100 operations per second. A modern "commodity" microprocessor (as of 2007) can process billions of operations per second, and many of these operations are more complicated and useful than early computer operations.
3. ^ "Heron of Alexandria". Retrieved on 2008-01-15.
4. ^ The Analytical Engine should not be confused with Babbage's difference engine which was a non-programmable mechanical calculator.
5. ^ B. Jack Copeland, ed., Colossus: The Secrets of Bletchley Park's Codebreaking Computers, Oxford University Press, 2006
6. ^ This program was written similarly to those for the PDP-11 minicomputer and shows some typical things a computer can do. All the text after the semicolons are comments for the benefit of human readers. These have no significance to the computer and are ignored. (Digital Equipment Corporation 1972)
7. ^ Attempts are often made to create programs that can overcome this fundamental limitation of computers. Software that mimics learning and adaptation is part of artificial intelligence.
8. ^ It is not universally true that bugs are solely due to programmer oversight. Computer hardware may fail or may itself have a fundamental problem that produces unexpected results in certain situations. For instance, the Pentium FDIV bug caused some Intel microprocessors in the early 1990s to produce inaccurate results for certain floating point division operations. This was caused by a flaw in the microprocessor design and resulted in a partial recall of the affected devices.
9. ^ Even some later computers were commonly programmed directly in machine code. Some minicomputers like the DEC PDP-8 could be programmed directly from a panel of switches. However, this method was usually used only as part of the booting process. Most modern computers boot entirely automatically by reading a boot program from some non-volatile memory.
10. ^ However, there is sometimes some form of machine language compatibility between different computers. An x86-64 compatible microprocessor like the AMD Athlon 64 is able to run most of the same programs that an Intel Core 2 microprocessor can, as well as programs designed for earlier microprocessors like the Intel Pentiums and Intel 80486. This contrasts with very early commercial computers, which were often one-of-a-kind and totally incompatible with other computers.
11. ^ High level languages are also often interpreted rather than compiled. Interpreted languages are translated into machine code on the fly by another program called an interpreter.
12. ^ Although this is a simple program, it contains a software bug. If the traffic signal is showing red when someone switches the "flash red" switch, it will cycle through green once more before starting to flash red as instructed. This bug is quite easy to fix by changing the program to repeatedly test the switch throughout each "wait" period—but writing large programs that have no bugs is exceedingly difficult.
13. ^ The control unit's rule in interpreting instructions has varied somewhat in the past. While the control unit is solely responsible for instruction interpretation in most modern computers, this is not always the case. Many computers include some instructions that may only be partially interpreted by the control system and partially interpreted by another device. This is especially the case with specialized computing hardware that may be partially self-contained. For example, EDVAC, the first modern stored program computer to be designed, used a central control unit that only interpreted four instructions. All of the arithmetic-related instructions were passed on to its arithmetic unit and further decoded there.
14. ^ Instructions often occupy more than one memory address, so the program counters usually increases by the number of memory locations required to store one instruction.
15. ^ Flash memory also may only be rewritten a limited number of times before wearing out, making it less useful for heavy random access usage. (Verma 1988)
16. ^ However, it is also very common to construct supercomputers out of many pieces of cheap commodity hardware; usually individual computers connected by networks. These so-called computer clusters can often provide supercomputer performance at a much lower cost than customized designs. While custom architectures are still used for most of the most powerful supercomputers, there has been a proliferation of cluster computers in recent years. (TOP500 2006)
17. ^ Most major 64-bit instruction set architectures are extensions of earlier designs. All of the architectures listed in this table existed in 32-bit forms before their 64-bit incarnations were introduced.
References
* a Kempf, Karl (1961). "Historical Monograph: Electronic Computers Within the Ordnance Corps". Aberdeen Proving Ground (United States Army).
* a Phillips, Tony (2000). "The Antikythera Mechanism I". American Mathematical Society. Retrieved on 2006-04-05.
* a Shannon, Claude Elwood (1940). "A symbolic analysis of relay and switching circuits". Massachusetts Institute of Technology.
* a Digital Equipment Corporation (1972). PDP-11/40 Processor Handbook (PDF), Maynard, MA: Digital Equipment Corporation.
* a Verma, G.; Mielke, N. (1988). "Reliability performance of ETOX based flash memories". IEEE International Reliability Physics Symposium.
* a Meuer, Hans; Strohmaier, Erich; Simon, Horst; Dongarra, Jack (2006-11-13). "Architectures Share Over Time". TOP500. Retrieved on 2006-11-27.
* Stokes, Jon (2007). Inside the Machine: An Illustrated Introduction to Microprocessors and Computer Architecture. San Francisco: No Starch Press. ISBN 978-1-59327-104-6.
Retrieved from "http://en.wikipedia.org/wiki/Computer"
Categories: Computing
Hidden categories: Semi-protected | Articles needing additional references from July 2008 | All articles with unsourced statements | Articles with unsourced statements since December 2007
Views
* Article
* Discussion
* View source
* History
Personal tools
* Log in / create account
Navigation
* Main Page
* Contents
* Featured content
* Current events
* Random article
Search
Interaction
* About Wikipedia
* Community portal
* Recent changes
* Contact Wikipedia
* Donate to Wikipedia
* Help
Toolbox
* What links here
* Related changes
* Upload file
* Special pages
* Printable version
* Permanent link
* Cite this page
Languages
* Afrikaans
* አማርኛ
* Anglo-Saxon
* العربية
* Aragonés
* Asturianu
* Azərbaycan
* বাংলা
* Bân-lâm-gú
* Башҡорт
* Беларуская (тарашкевіца)
* Boarisch
* Bosanski
* Brezhoneg
* Български
* Català
* Чăвашла
* Česky
* Cymraeg
* Dansk
* Deutsch
* Diné bizaad
* Eesti
* Ελληνικά
* Español
* Esperanto
* Euskara
* فارسی
* Føroyskt
* Français
* Frysk
* Furlan
* Gaeilge
* Gàidhlig
* Galego
* ������������
* 한국어
* Հայերեն
* हिन्दी
* Hrvatski
* Ido
* ইমার ঠার/বিষ্ণুপ্রিয়া মণিপুরী
* Bahasa Indonesia
* Interlingua
* ᐃᓄᒃᑎᑐᑦ/inuktitut
* isiZulu
* Íslenska
* Italiano
* עברית
* Basa Jawa
* ಕನ್ನಡ
* ქართული
* Қазақша
* Kernewek
* Kiswahili
* Kongo
* Kurdî / كوردی
* ລາວ
* Latina
* Latviešu
* Lëtzebuergesch
* Lietuvių
* Limburgs
* Lingála
* Magyar
* Македонски
* Malagasy
* മലയാളം
* Malti
* मराठी
* Bahasa Melayu
* Монгол
* Myanmasa
* Nahuatl
* Nederlands
* Nedersaksisch
* नेपाली
* नेपाल भाषा
* 日本語
* Nnapulitano
* Norsk (bokmål)
* Norsk (nynorsk)
* Occitan
* O'zbek
* ਪੰਜਾਬੀ
* Plattdüütsch
* Polski
* Português
* Română
* Runa Simi
* Русский
* Scots
* Shqip
* Sicilianu
* සිංහල
* Simple English
* Slovenčina
* Словѣ́ньскъ / ⰔⰎⰑⰂⰡⰐⰠⰔⰍⰟ
* Slovenščina
* Soomaaliga
* Српски / Srpski
* Srpskohrvatski / Српскохрватски
* Basa Sunda
* Suomi
* Svenska
* Tagalog
* தமிழ்
* తెలుగు
* ไทย
* Tiếng Việt
* Тоҷикӣ/tojikī
* Türkçe
* Українська
* اردو
* Vèneto
* Walon
* Wolof
* ייִדיש
* 粵語
* Zazaki
* Žemaitėška
* 中文
Powered by MediaWiki
Wikimedia Foundation
Monday, July 14, 2008
Music
Music is an art form in which the medium is sound organized in time. Common elements of music are pitch (which governs melody and harmony), rhythm (and its associated concepts tempo, meter, and articulation), dynamics, and the sonic qualities of timbre and texture. The word derives from Greek μουσική (mousike), "(art) of the Muses".[1]
Contents
[hide]
* 1 Definition of music
* 2 History
o 2.1 Ancient
o 2.2 Medieval and Renaissance Europe
o 2.3 European Baroque
o 2.4 European Classical
o 2.5 Romantic
o 2.6 20th century
* 3 Performance
o 3.1 Aural tradition
o 3.2 Ornamentation
* 4 Production
o 4.1 Composition
o 4.2 Notation
o 4.3 Improvisation
o 4.4 Theory
* 5 Cognition
* 6 Sociology
* 7 Media and technology
o 7.1 Internet
* 8 Business
* 9 Education
o 9.1 Primary
o 9.2 Academia
o 9.3 Ethnomusicology
* 10 Music therapy
* 11 See also
* 12 References
* 13 Further reading
* 14 External links
Definition of music
See also: Music genre
Musical notations
Musical notations
Greek philosophers and ancient Indians defined music as tones ordered horizontally as melodies and vertically as harmonies. Music theory, within this realm, is studied with the presupposition that music is orderly and often pleasant to hear. However, in the 20th century, composers challenged the notion that music had to be pleasant by creating music that explored harsher, darker timbres. The existence of some modern-day music genres such as death metal and grindcore, which enjoy an extensive underground following, indicate that even the harshest sounds can be considered music if the listener is so inclined.
20th-century composer John Cage disagreed with the notion that music must consist of pleasant, discernible melodies. Instead, he argued that any sounds we can hear can be music, saying, for example, "There is no noise, only sound."[2] According to musicologist Jean-Jacques Nattiez, "the border between music and noise is always culturally defined—which implies that, even within a single society, this border does not always pass through the same place; in short, there is rarely a consensus.… By all accounts there is no single and intercultural universal concept defining what music might be, except that it is 'sound through time'."[3]
The creation, performance, significance, and even the definition of music vary according to culture and social context. Music ranges from strictly organized compositions (and their recreation in performance), through improvisational music to aleatoric forms. Music can be divided into genres and subgenres, although the dividing lines and relationships between music genres are often subtle, sometimes open to individual interpretation, and occasionally controversial. Within "the arts", music can be classified as a performing art, a fine art, or an auditory art form.
History
Figurines playing stringed instruments, excavated at Susa, 2nd millennium BC. Iran National Museum.
Figurines playing stringed instruments, excavated at Susa, 2nd millennium BC. Iran National Museum.
Main article: History of music
The development of music among humans must have taken place against the backdrop of natural sounds such as birdsong and the sounds other animals use to communicate.[citation needed] Prehistoric music is the name which is given to all music produced in preliterate cultures.[citation needed][4]
Ancient
Globe icon
The examples and perspective in this article or section may not represent a worldwide view of the subject.
Please improve this article or discuss the issue on the talk page.
Main article: Ancient music
A range of paleolithic sites have yielded bones in which lateral holes have been pierced: these are usually identified as flutes,[5] blown at one end like the Japanese shakuhachi. The earliest written records of musical expression are to be found in the Samaveda of India and in 4,000 year old cuneiform from Ur.[citation needed] Instruments, such as the seven-holed flute and various types of stringed instruments have been recovered from the Indus Valley Civilization archaeological sites.[6] India has one of the oldest musical traditions in the world—references to Indian classical music (marga) can be found in the ancient scriptures of the Hindu tradition, the Vedas. The traditional art or court music of China has a history stretching for more than three thousand years. Music was an important part of cultural and social life in Ancient Greece: mixed-gender choruses performed for entertainment, celebration and spiritual ceremonies; musicians and singers had a prominent role in ancient Greek theater
In the 9th century, al-Farabi wrote a notable book on music titled Kitab al-Musiqi al-Kabir ("Great Book of Music"). He played and invented a variety of musical instruments and devised the Arab tone system of pitch organisation, which is still used in Arabic music.[7]
Medieval and Renaissance Europe
Main articles: Medieval music and Renaissance music
While musical life in Europe was undoubtedly rich in the early Medieval era, as attested by artistic depictions of instruments, writings about music, and other records, the only European repertory which has survived from before about 800 is the monophonic liturgical plainsong of the Roman Catholic Church, the central tradition of which was called Gregorian chant. Several schools of liturgical polyphony flourished beginning in the 12th century. Alongside these traditions of sacred music, a vibrant tradition of secular song developed, exemplified by the music of the troubadours, trouvères and Minnesänger.
Much of the surviving music of 14th century Europe is secular. By the middle of the 15th century, composers and singers used a smooth polyphony for sacred musical compositions such as the mass, the motet, and the laude, and secular forms such as the chanson and the madrigal. The introduction of commercial printing had an immense influence on the dissemination of musical styles.[citation needed]
European Baroque
Main article: Baroque music
The first operas, written around 1600 and the rise of contrapuntal music define the end of the Renaissance and the beginning of the Baroque era that lasted until roughly 1750, the year of the death of Johann Sebastian Bach.
Allegory of Music, by Filippino Lippi
Allegory of Music, by Filippino Lippi
Allegory of Music on the Opéra Garnier
Allegory of Music on the Opéra Garnier
German Baroque composers wrote for small ensembles including strings, brass, and woodwinds, as well as choirs, pipe organ, harpsichord, and clavichord. During the Baroque period, several major music forms were defined that lasted into later periods when they were expanded and evolved further, including the fugue, the invention, the sonata, and the concerto.[8]
European Classical
Main article: Classical period (music)
The music of the Classical period is characterized by homophonic texture, often featuring a prominent melody with accompaniment. These new melodies tended to be almost voice-like and singable. The now popular instrumental music was dominated by further evolution of musical forms initially defined in the Baroque period: the sonata, and the concerto, with the addition of the new form, the symphony. Joseph Haydn and Wolfgang Amadeus Mozart, well known even today, are among the central figures of the Classical period.
Romantic
Main article: Romantic music
Ludwig van Beethoven and Franz Schubert were transitional composers, leading into the Romantic period, with their expansion of existing genres, forms, and functions of music. In the Romantic period, the emotional and expressive qualities of music came to take precedence over the orientation towards technique and tradition. The late 19th century saw a dramatic expansion in the size of the orchestra, and in the role of concerts as part of urban society. Later Romantic composers created complex and often much longer musical works, merging and expanding traditional forms that had previously been used separately. For example, counterpoint, combined with harmonic structures to create more extended chords with increased use of dissonance and to create dramatic tension and resolution.
20th century
Main article: 20th century music
In the 20th century there was a vast increase in music listening as the radio gained popularity worldwide and new media and technologies were developed to record, capture, reproduce and distribute music. The focus of art music was characterized by exploration. Claude Debussy has become well-known and respected for his orientation towards colors and depictions in his compositional style. Igor Stravinsky, Arnold Schoenberg, and John Cage were all influential composers in 20th century art music. Jazz evolved and became a significant genre of music over the course of the 20th century, and during the second half of that century, rock music and hip hop music did the same.
Performance
Main article: Performance
Chinese Naxi musicians
Chinese Naxi musicians
Performance is the physical expression of music. Often, a musical work is performed once its structure and instrumentation are satisfactory to its creators; however, as it gets performed, it can evolve and change.
A performance can either be rehearsed or improvised. Improvisation is a musical idea created on the spot (such as a guitar solo or a drum solo), with no prior premeditation, while rehearsal is vigorous repetition of an idea until it has achieved cohesion. Musicians will generally add improvisation to a well-rehearsed idea to create a unique performance.
Many cultures include strong traditions of solo and performance, such as in Indian classical music, and in the Western Art music tradition. Other cultures, such as in Bali, include strong traditions of group performance. All cultures include a mixture of both, and performance may range from improvised solo playing for one's enjoyment to highly planned and organised performance rituals such as the modern classical concert, religious processions, music festivals or music competitions.
Chamber music, which is music for a small ensemble with only a few of each type of instrument, is often seen as more intimate than symphonic works. A performer may be referred to as a musician.
Aural tradition
Many types of music, such as traditional blues and folk music were originally preserved in the memory of performers, and the songs were handed down orally, or aurally (by ear). When the composer of music is no longer known, this music is often classified as "traditional". Different musical traditions have different attitudes towards how and where to make changes to the original source material, from quite strict, to those which demand improvisation or modification to the music. A culture's history may also be passed by ear through song.
Ornamentation
Main article: Ornament (music)
The detail included explicitly in the music notation varies between genres and historical periods. In general, art music notation from the 17th through the 19th century required performers to have a great deal of contextual knowledge about performing styles.
For example, in the 17th and 18th century, music notated for solo performers typically indicated a simple, unornamented melody. However, it was expected that performers would know how to add stylistically-appropriate ornaments such as trills and turns. In the 19th century, art music for solo performers may give a general instruction such as to perform the music expressively, without describing in detail how the performer should do this. It was expected that the performer would know how to use tempo changes, accentuation, and pauses (among other devices) to obtain this "expressive" performance style. In the 20th century, art music notation often became more explicit and used a range of markings and annotations to indicate to performers how they should play or sing the piece.
In popular music and jazz, music notation almost always indicates only the basic framework of the melody, harmony, or performance approach; musicians and singers are expected to know the performance conventions and styles associated with specific genres and pieces. For example, the "lead sheet" for a jazz tune may only indicate the melody and the chord changes. The performers in the jazz ensemble are expected to know how to "flesh out" this basic structure by adding ornaments, improvised music, and chordal accompaniment.
Production
Main article: Music production
Music is composed and performed for many purposes, ranging from aesthetic pleasure, religious or ceremonial purposes, or as an entertainment product for the marketplace. Amateur musicians compose and perform music for their own pleasure, and they do not derive their income from music. Professional musicians are employed by a range of institutions and organisations, including armed forces, churches and synagogues, symphony orchestras, broadcasting or film production companies, and music schools. Professional musicians sometimes work as freelancers, seeking contracts and engagements in a variety of settings.
There are often many links between amateur and professional musicians. Beginning amateur musicians take lessons with professional musicians. In community settings, advanced amateur musicians perform with professional musicians in a variety of ensembles and orchestras. In some cases, amateur musicians attain a professional level of competence, and they are able to perform in professional performance settings.
A distinction is often made between music performed for the benefit of a live audience and music that is performed for the purpose of being recorded and distributed through the music retail system or the broadcasting system. However, there are also many cases where a live performance in front of an audience is recorded and distributed (or broadcast).
Composition
Main article: Musical composition
"Composition" is often classed as the creation and recording of music via a medium by which others can interpret it (i.e. paper or sound). Many cultures use at least part of the concept of preconceiving musical material, or composition, as held in western classical music. Even when music is notated precisely, there are still many decisions that a performer has to make. The process of a performer deciding how to perform music that has been previously composed and notated is termed interpretation.
Different performers' interpretations of the same music can vary widely. Composers and song writers who present their own music are interpreting, just as much as those who perform the music of others or folk music. The standard body of choices and techniques present at a given time and a given place is referred to as performance practice, where as interpretation is generally used to mean either individual choices of a performer, or an aspect of music which is not clear, and therefore has a "standard" interpretation.
In some musical genres, such as jazz and blues, even more freedom is given to the performer to engage in improvisation on a basic melodic, harmonic, or rhythmic framework. The greatest latitude is given to the performer in a style of performing called free improvisation, which is material that is spontaneously "thought of" (imagined) while being performed, not preconceived. According to the analysis of Georgiana Costescu,[citation needed] improvised music usually follows stylistic or genre conventions and even "fully composed" includes some freely chosen material. Composition does not always mean the use of notation, or the known sole authorship of one individual.
Music can also be determined by describing a "process" which may create musical sounds; examples of this range from wind chimes, through computer programs which select sounds. Music which contains elements selected by chance is called Aleatoric music, and is associated with such composers as John Cage, Morton Feldman, and Witold Lutosławski.
Musical composition is a term that describes the composition of a piece of music. Methods of composition vary widely from one composer to another, however in analysing music all forms — spontaneous, trained, or untrained — are built from elements comprising a musical piece. Music can be composed for repeated performance or it can be improvised: composed on the spot. The music can be performed entirely from memory, from a written system of musical notation, or some combination of both. Study of composition has traditionally been dominated by examination of methods and practice of Western classical music, but the definition of composition is broad enough to include spontaneously improvised works like those of free jazz performers and African drummers such as the Ewe drummers.
What is important in understanding the composition of a piece is singling out its elements. An understanding of music's formal elements can be helpful in deciphering exactly how a piece is constructed. A universal element of music is how sounds occur in time, which is referred to as the rhythm of a piece of music.
When a piece appears to have a changing time-feel, it is considered to be in rubato time, an Italian expression that indicates that the tempo of the piece changes to suit the expressive intent of the performer. Even random placement of random sounds, which occurs in musical montage, occurs within some kind of time, and thus employs time as a musical element.
Notation
Main article: Musical notation
Notation is the written expression of music notes and rhythms on paper using symbols. When music is written down, the pitches and rhythm of the music is notated, along with instructions on how to perform the music. The study of how to read notation involves music theory, harmony, the study of performance practice, and in some cases an understanding of historical performance methods.
Written notation varies with style and period of music. In Western Art music, the most common types of written notation are scores, which include all the music parts of an ensemble piece, and parts, which are the music notation for the individual performers or singers. In popular music, jazz, and blues, the standard musical notation is the lead sheet, which notates the melody, chords, lyrics (if it is a vocal piece), and structure of the music. Scores and parts are also used in popular music and jazz, particularly in large ensembles such as jazz "big bands."
In popular music, guitarists and electric bass players often read music notated in tablature, which indicates the location of the notes to be played on the instrument using a diagram of the guitar or bass fingerboard. Tabulature was also used in the Baroque era to notate music for the lute, a stringed, fretted instrument.
Notated music is produced as sheet music. To perform music from notation requires an understanding of both the musical style and the performance practice that is associated with a piece of music or genre.
Improvisation
Main article: Musical improvisation
Improvisation is the creation of spontaneous music. Improvisation is often considered an act of instantaneous composition by composers, where compositional techniques are employed with or without preparation.
Theory
Main article: Music theory
Music theory encompasses the nature and mechanics of music. It often involves identifying patterns that govern composers' techniques. In a more detailed sense, music theory (in the western system) also distills and analyzes the elements of music – rhythm, harmony (harmonic function), melody, structure, and texture. People who study these properties are known as music theorists.
Cognition
Further information: Hearing (sense) and Psychoacoustics
Concert in the Mozarteum, Salzburg
Concert in the Mozarteum, Salzburg
The field of music cognition involves the study of many aspects of music including how it is processed by listeners. Rather than accepting the standard practices of analyzing, composing, and performing music as a given, much research in music cognition seeks instead to uncover the mental processes that underlie these practices. Also, research in the field seeks to uncover commonalities between the musical traditions of disparate cultures and possible cognitive "constraints" that limit these musical systems. Questions regarding musical innateness, and emotional responses to music are also major areas of research in the field.
Deaf people can experience music by feeling the vibrations in their body, a process which can be enhanced if the individual holds a resonant, hollow object. A well-known deaf musician is the composer Ludwig van Beethoven, who composed many famous works even after he had completely lost his hearing. Recent examples of deaf musicians include Evelyn Glennie, a highly acclaimed percussionist who has been deaf since age twelve, and Chris Buck, a virtuoso violinist who has lost his hearing. This is relevant because it indicates that music is a deeper cognitive process than unexamined phrases such as, "pleasing to the ear" would suggest. Much research in music cognition seeks to uncover these complex mental processes involved in listening to music, which may seem intuitively simple, yet are vastly intricate and complex.
Sociology
Half-section of the Song Dynasty (960–1279) version of Night Revels of Han Xizai, original by Gu Hongzhong; the painting shows musicians entertaining guests in a 10th century household. In the center are three female musicians playing guan, two female musicians playing transverse bamboo flutes, and a male musician playing a wooden clapper called paiban.
Half-section of the Song Dynasty (960–1279) version of Night Revels of Han Xizai, original by Gu Hongzhong; the painting shows musicians entertaining guests in a 10th century household. In the center are three female musicians playing guan, two female musicians playing transverse bamboo flutes, and a male musician playing a wooden clapper called paiban.
Music is experienced by individuals in a range of social settings ranging from being alone to attending a large concert. Musical performances take different forms in different cultures and socioeconomic milieus. In Europe and North America, there is often a divide between what types of music are viewed as a "high culture" and "low culture." "High culture" types of music typically include Western art music such as Baroque, Classical, Romantic, and modern-era symphonies, concertos, and solo works, and are typically heard in formal concerts in concert halls and churches, with the audience sitting quietly in seats.
Other types of music - including, but not limited to, jazz, blues, soul, and country - are often performed in bars, nightclubs, and theatres, where the audience may be able to drink, dance, and express themselves by cheering. Until the later 20th century, the division between "high" and "low" musical forms was widely accepted as a valid distinction that separated out better quality, more advanced "art music" from the popular styles of music heard in bars and dance halls.
However, in the 1980s and 1990s, musicologists studying this perceived divide between "high" and "low" musical genres argued that this distinction is not based on the musical value or quality of the different types of music.[citation needed] Rather, they argued that this distinction was based largely on the socioeconomic standing or social class of the performers or audience of the different types of music.[citation needed] For example, whereas the audience for Classical symphony concerts typically have above-average incomes, the audience for a rap concert in an inner-city area may have below-average incomes. Even though the performers, audience, or venue where non-"art" music is performed may have a lower socioeconomic status, the music that is performed, such as blues, rap, punk, funk, or ska may be very complex and sophisticated.
When composers introduce styles of music which break with convention, there can be a strong resistance from academic music experts and popular culture. Late-period Beethoven string quartets, Stravinsky ballet scores, serialism, bebop-era jazz, hip hop, punk rock, and electronica have all been considered non-music by some critics when they were first introduced.[citation needed]
Such themes are examined in the sociology of music. The sociological study of music, sometimes called sociomusicology, is often pursued in departments of sociology, media studies, or music, and is closely related to the field of ethnomusicology.
Media and technology
Further information: Computer music
The music that composers make can be heard through several media; the most traditional way is to hear it live, in the presence, or as one of the musicians. Live music can also be broadcast over the radio, television or the Internet. Some musical styles focus on producing a sound for a performance, while others focus on producing a recording which mixes together sounds which were never played "live". Recording, even of styles which are essentially live, often uses the ability to edit and splice to produce recordings which are considered better than the actual performance.
As talking pictures emerged in the early 20th century, with their prerecorded musical tracks, an increasing number of moviehouse orchestra musicians found themselves out of work.[9] During the 1920s live musical performances by orchestras, pianists, and theater organists were common at first-run theaters.[10] With the coming of the talking motion pictures, those featured performances were largely eliminated. The American Federation of Musicians (AFM) took out newspaper advertisements protesting the replacement of live musicians with mechanical playing devices. One 1929 ad that appeared in the Pittsburgh Press features an image of a can labeled "Canned Music / Big Noise Brand / Guaranteed to Produce No Intellectual or Emotional Reaction Whatever"[11]
Since legislation introduced to help protect performers, composers, publishers and producers, including the Audio Home Recording Act of 1992 in the United States, and the 1979 revised Berne Convention for the Protection of Literary and Artistic Works in the United Kingdom, recordings and live performances have also become more accessible through computers, devices and Internet in a form that is commonly known as Music-On-Demand.
In many cultures, there is less distinction between performing and listening to music, since virtually everyone is involved in some sort of musical activity, often communal. In industrialized countries, listening to music through a recorded form, such as sound recording or watching a music video, became more common than experiencing live performance, roughly in the middle of the 20th century.
Sometimes, live performances incorporate prerecorded sounds. For example, a disc jockey uses disc records for scratching, and some 20th century works have a solo for an instrument or voice that is performed along with music that is prerecorded onto a tape. Computers and many keyboards can be programmed to produce and play Musical Instrument Digital Interface (MIDI) music. Audiences can also become performers by participating in karaoke, an activity of Japanese origin which centres around a device that plays voice-eliminated versions of well-known songs. Most karaoke machines also have video screens that show lyrics to songs being performed; performers can follow the lyrics as they sing over the instrumental tracks.
Internet
The advent of the Internet has transformed the experience of music, partly through the increased ease of access to music and the increased choice. Chris Anderson, in his book The Long Tail: Why the Future of Business is Selling Less of More, suggests that while the economic model of supply and demand describes scarcity, the Internet retail model is based on abundance. Digital storage costs are low, so a company can afford to make its whole inventory available online, giving customers as much choice as possible. It has thus become economically viable to offer products that very few people are interested in. Consumers' growing awareness of their increased choice results in a closer association between listening tastes and social identity, and the creation of thousands of niche markets.[12]
Another effect of the Internet arises with online communities like YouTube and MySpace. MySpace has made social networking with other musicians easier, and greatly facilitates the distribution of one's music. YouTube also has a large community of both amateur and professional musicians who post videos and comments.[citation needed] Professional musicians also use YouTube as a free publisher of promotional material.
YouTube users, for example, no longer only download and listen to MP3s, but also actively create their own. According to Don Tapscott and Anthony D. Williams, in their book Wikinomics, there has been a shift from a traditional consumer role to what they call a "prosumer" role, a consumer who both creates and consumes. Manifestations of this in music include the production of mashes, remixes, and music videos by fans.[13]
Business
Main article: Music industry
The music industry refers to the business industry connected with the creation and sale of music. It consists of record companies, labels and publishers that distribute recorded music products internationally and that often control the rights to those products. Some music labels are "independent," while others are subsidiaries of larger corporate entities or international media groups.
Education
Primary
Main article: Music education
The incorporation of music training from preschool to post secondary education is common in North America and Europe. Involvement in music is thought to teach basic skills such as concentration, counting, listening, and cooperation while also promoting understanding of language, improving the ability to recall information, and creating an environment more conducive to learning in other areas.[14] In elementary schools, children often learn to play instruments such as the recorder, sing in small choirs, and learn about the history of Western art music. In secondary schools students may have the opportunity to perform some type of musical ensembles, such as choirs, marching bands, concert bands, jazz bands, or orchestras, and in some school systems, music classes may be available. Some students also take private music lessons with a teacher. Amateur musicians typically take lessons to learn musical rudiments and beginner- to intermediate-level musical techniques.
At the university level, students in most arts and humanities programs can receive credit for taking music courses, which typically take the form of an overview course on the history of music, or a music appreciation course that focuses on listening to music and learning about different musical styles. In addition, most North American and European universities have some type of musical ensembles that non-music students are able to participate in, such as choirs, marching bands, or orchestras. The study of Western art music is increasingly common outside of North America and Europe, such as the Indonesian Institute of the Arts in Yogyakarta, Indonesia, or the classical music programs that are available in Asian countries such as South Korea, Japan, and China. At the same time, Western universities and colleges are widening their curriculum to include music of non-Western cultures, such as the music of Africa or Bali (e.g. Gamelan music).
Academia
Musicology is the study of the subject of music. The earliest definitions defined three sub-disciplines: systematic musicology, historical musicology, and comparative musicology or ethnomusicology. In contemporary scholarship, one is more likely to encounter a division of the discipline into music theory, music history, and ethnomusicology. Research in musicology has often been enriched by cross-disciplinary work, for example in the field of psychoacoustics. The study of music of non-western cultures, and the cultural study of music, is called ethnomusicology.
Graduates of undergraduate music programs can go on to further study in music graduate programs. Graduate degrees include the Master of Music, the Master of Arts, the Doctor of Philosophy (PhD) (e.g., in musicology or music theory), and more recently, the Doctor of Musical Arts, or DMA. The Master of Music degree, which takes one to two years to complete, is typically awarded to students studying the performance of an instrument, education, voice or composition. The Master of Arts degree, which takes one to two years to complete and often requires a thesis, is typically awarded to students studying musicology, music history, or music theory. Undergraduate university degrees in music, including the Bachelor of Music, the Bachelor of Music Education, and the Bachelor of Arts (with a major in music) typically take three to five years to complete. These degrees provide students with a grounding in music theory and music history, and many students also study an instrument or learn singing technique as part of their program.
The PhD, which is required for students who want to work as university professors in musicology, music history, or music theory, takes three to five years of study after the Master's degree, during which time the student will complete advanced courses and undertake research for a dissertation. The DMAis a relatively new degree that was created to provide a credential for professional performers or composers that want to work as university professors in musical performance or composition. The DMA takes three to five years after a Master's degree, and includes advanced courses, projects, and performances. In Medieval times, the study of music was one of the Quadrivium of the seven Liberal Arts and considered vital to higher learning. Within the quantitative Quadrivium, music, or more accurately harmonics, was the study of rational proportions.
Zoomusicology is the study of the music of non-human animals, or the musical aspects of sounds produced by non-human animals. As George Herzog (1941) asked, "do animals have music?" François-Bernard Mâche's Musique, mythe, nature, ou les Dauphins d'Arion (1983), a study of "ornitho-musicology" using a technique of Nicolas Ruwet's Language, musique, poésie (1972) paradigmatic segmentation analysis, shows that bird songs are organised according to a repetition-transformation principle. Jean-Jacques Nattiez (1990), argues that "in the last analysis, it is a human being who decides what is and is not musical, even when the sound is not of human origin. If we acknowledge that sound is not organised and conceptualised (that is, made to form music) merely by its producer, but by the mind that perceives it, then music is uniquely human."
Music theory is the study of music, generally in a highly technical manner outside of other disciplines. More broadly it refers to any study of music, usually related in some form with compositional concerns, and may include mathematics, physics, and anthropology. What is most commonly taught in beginning music theory classes are guidelines to write in the style of the common practice period, or tonal music. Theory, even that which studies music of the common practice period, may take many other forms. Musical set theory is the application of mathematical set theory to music, first applied to atonal music. Speculative music theory, contrasted with analytic music theory, is devoted to the analysis and synthesis of music materials, for example tuning systems, generally as preparation for composition.
Ethnomusicology
Main article: Ethnomusicology
In the West, much of the history of music that is taught deals with the Western civilization's art music. The history of music in other cultures ("world music" or the field of "ethnomusicology") is also taught in Western universities. This includes the documented classical traditions of Asian countries outside the influence of Western Europe, as well as the folk or indigenous music of various other cultures.
Popular styles of music varied widely from culture to culture, and from period to period. Different cultures emphasised different instruments, or techniques, or uses for music. Music has been used not only for entertainment, for ceremonies, and for practical and artistic communication, but also for propaganda in totalitarian countries.
There is a host of music classifications, many of which are caught up in the argument over the definition of music. Among the largest of these is the division between classical music (or "art" music), and popular music (or commercial music - including rock and roll, country music, and pop music). Some genres don't fit neatly into one of these "big two" classifications, (such as folk music, world music, or jazz music).
As world cultures have come into greater contact, their indigenous musical styles have often merged into new styles. For example, the United States bluegrass style contains elements from Anglo-Irish, Scottish, Irish, German and African instrumental and vocal traditions, which were able to fuse in the United States' multi-ethnic society. Genres of music are determined as much by tradition and presentation as by the actual music. Some works, like George Gershwin's Rhapsody in Blue, are claimed by both jazz and classical music. Many current music festivals celebrate a particular musical genre.
Indian music, for example, is one of the oldest and longest living types of music, and is still widely heard and performed in South Asia, as well as internationally (especially since the 1960s). Indian music has mainly 3 forms of classical music, Hindustani, Carnatic, and Dhrupad styles. It has also a large repertoire of styles, which involve only percussion music such as the talavadya performances famous in South India.
Music therapy
Main article: Music therapy
Robert Burton wrote in his 17th century work, The Anatomy of Melancholy, that music and dance were critical in treating mental illness, especially melancholia.[15] He said that
But to leave all declamatory speeches in praise of divine music, I will confine myself to my proper subject: besides that excellent power it hath to expel many other diseases, it is a sovereign remedy against despair and melancholy, and will drive away the devil himself.
Burton noted that
...Canus, a Rhodian fiddler, in Philostratus, when Apollonius was inquisitive to know what he could do with his pipe, told him, "That he would make a melancholy man merry, and him that was merry much merrier than before, a lover more enamoured, a religious man more devout."
[16][17][18]
In November 2006, Dr. Michael J. Crawford[19] and his colleagues also found that music therapy helped schizophrenic patients.[20] In the Ottoman Empire, mental illnesses were treated with music.[21]
See also
Music portal
* List of basic music topics
* List of music topics
References
1. ^ Mousike, Henry George Liddell, Robert Scott, A Greek-English Lexicon, at Perseus
2. ^ John Cage, 79, a Minimalist Enchanted With Sound, Dies
3. ^ Nattiez 1990: 47-8, 55
4. ^ "Primitive music" is an obsolescent term for prehistoric music.[citation needed]
5. ^ Son et musique au paléolithique", Pour La Science,. 253, 52-58 (1998)
6. ^ The Music of India By Reginald MASSEY, Jamila MASSEY. Google Books
7. ^ Touma (1996), p.170
8. ^ Baroque Music by Elaine Thornburgh and Jack Logan, Ph. D.
9. ^ American Federation of Musicians/History
10. ^ Hubbard (1985), p. 429.
11. ^ "Canned Music on Trial" part of Duke University's Ad*Access project.
12. ^ Anderson, Chris (2006). The Long Tail: Why the Future of Business is Selling Less of More. Hyperion. ISBN 1-4013-0237-8.
13. ^ Tapscott, Don; Williams, Anthony D. (2006-12-28). Wikinomics: How Mass Collaboration Changes Everything. Portfolio Hardcover. ISBN 978-1591841388.
14. ^ Woodall and Ziembroski, 2002
15. ^ cf. The Anatomy of Melancholy, Robert Burton, subsection 3, on and after line 3,480, "Music a Remedy"
16. ^ Ismenias the Theban, Chiron the centaur, is said to have cured this and many other diseases by music alone: as now thy do those, saith Bodine, that are troubled with St. Vitus's Bedlam dance. Project Gutenberg's The Anatomy of Melancholy, by Democritus Junior
17. ^ "Humanities are the Hormones: A Tarantella Comes to Newfoundland. What should we do about it?" by Dr. John Crellin, MUNMED, newsletter of the Faculty of Medicine, Memorial University of Newfoundland, 1996.
18. ^ Aung, Steven K.H., Lee, Mathew H.M., "Music, Sounds, Medicine, and Meditation: An Integrative Approach to the Healing Arts", Alternative & Complementary Therapies, Oct 2004, Vol. 10, No. 5: 266-270.
19. ^ Dr. Michael J. Crawford page at Imperial College London, Faculty of Medicine, Department of Psychological Medicine.
20. ^ Crawford, Mike J.; Talwar, Nakul, et al. (November 2006). "Music therapy for in-patients with schizophrenia: Exploratory randomised controlled trial". The British Journal of Psychiatry (2006) 189: 405–409. doi:10.1192/bjp.bp.105.015073. PMID 17077429.
21. ^ Treatment of Mental Illnesses With Music Therapy - A different approach from history
Further reading
* Harwood, Dane (1976). "Universals in Music: A Perspective from Cognitive Psychology", Ethnomusicology 20, no. 3:521-33.
* Johnson, Julian (2002). Who Needs Classical Music?: Cultural Choice and Musical Value. Oxford University Press. ISBN 0-19-514681-6.
* Kertz-Welzel, Alexandra. "Piano Improvisation Develops Musicianship." Orff-Echo XXXVII No. 1 (2004): 11-14.
* Kertz-Welzel, Alexandra. "The Singing Muse: Three Centuries of Music Education in Germany." Journal of Historical Research in Music Education XXVI no. 1 (2004): 8-27.
* Kertz-Welzel, Alexandra. "Didaktik of Music: A German Concept and its Comparison to American Music Pedagogy." International Journal of Music Education (Practice) 22 No. 3 (2004): 277-286.
* Kertz-Welzel, Alexandra. "General Music Education in Germany Today: A Look at How Popular Music is Engaging Students." General Music Today 18 no. 2 (Winter 2005): 14-16.
* Molino, Jean (1975). "Fait musical et sémiologue de la musique", Musique en Jeu, no. 17:37-62.
* Nattiez, Jean-Jacques (1987). Music and Discourse: Toward a Semiology of Music (Musicologie générale et sémiologue, 1987). Translated by Carolyn Abbate (1979). ISBN 0-691-02714-5.
* Owen, Harold (2000). Music Theory Resource Book. Oxford University Press. ISBN 0-19-511539-2.
* Small, Christopher (1977). Music, Society, Education. John Calder Publishers, London. ISBN 0-7145-3614-8
* Habib Hassan Touma (1996). The Music of the Arabs, trans. Laurie Schwartz. Portland, Oregon: Amadeus Press. ISBN 0-931340-88-8
* Woodall, Laura and Brenda Ziembroski, (2002). Literacy Through Music.
External links
Find more about Music on Wikipedia's sister projects:
Dictionary definitions
Textbooks
Quotations
Source texts
Images and media
News stories
Learning resources
* BBC Blast Music For 13-19 year olds interested in learning about, making, performing and talking about music.
* The Virginia Tech Multimedia Music Dictionary, with definitions, pronunciations, examples, quizzes and simulations
* The Music-Web Music Encyclopedia, for musicians, composers and music lovers
* Dolmetsch free online music dictionary, complete, with references to a list of specialised music dictionaries (by continent, by instrument, by genre, etc.)
* "On Hermeneutical Ethics and Education: Bach als Erzieher", a paper by Prof. Miguel Ángel Quintana Paz in which he explains the history of the different views hold about music in Western societies, since the Ancient Greece to our days.
* Monthly Online Features From Bloomingdale School of Music, addressing a variety of musical topics for a wide audience
* Arts and Music Uplifting Society towards Transformation and Tolerance Articles meant to stimulate people’s awareness about the peace enhancing, transforming, communicative, educational and healing powers of music.
Retrieved from "http://en.wikipedia.org/wiki/Music"
Categories: Music | Sound | Greek loanwords
Hidden categories: All articles with unsourced statements | Articles with unsourced statements since November 2007 | Semi-protected against vandalism | Articles with limited geographic scope | Europe-centric | Articles with unsourced statements since March 2008 | Articles with unsourced statements since May 2007
Views
* Article
* Discussion
* View source
* History
Personal tools
* Log in / create account
Navigation
* Main Page
* Contents
* Featured content
* Current events
* Random article
Search
Interaction
* About Wikipedia
* Community portal
* Recent changes
* Contact Wikipedia
* Donate to Wikipedia
* Help
Toolbox
* What links here
* Related changes
* Upload file
* Special pages
* Printable version
* Permanent link
* Cite this page
Languages
* Afrikaans
* አማርኛ
* العربية
* Aragonés
* ܐܪܡܝܐ
* Asturianu
* Avañe'ẽ
* Bamanankan
* বাংলা
* Bân-lâm-gú
* Basa Banyumasan
* Беларуская
* Беларуская (тарашкевіца)
* Boarisch
* Bosanski
* Brezhoneg
* Български
* Català
* Чăвашла
* Cebuano
* Česky
* Corsu
* Cymraeg
* Dansk
* Deutsch
* ދިވެހިބަސް
* Eesti
* Ελληνικά
* Español
* Esperanto
* Euskara
* فارسی
* Føroyskt
* Français
* Frysk
* Furlan
* Gaeilge
* Gàidhlig
* Galego
* Hak-kâ-fa
* 한국어
* हिन्दी
* Hrvatski
* Ido
* Bahasa Indonesia
* Interlingua
* Interlingue
* Иронау
* Íslenska
* Italiano
* עברית
* Basa Jawa
* ಕನ್ನಡ
* ქართული
* कश्मीरी - (كشميري)
* Kernewek
* Кыргызча
* Kreyòl ayisyen
* Ladino
* ລາວ
* Latina
* Latviešu
* Lëtzebuergesch
* Lietuvių
* Líguru
* Limburgs
* Lojban
* Magyar
* മലയാളം
* Malti
* मराठी
* مَزِروني
* Bahasa Melayu
* Nahuatl
* Nederlands
* Nedersaksisch
* नेपाली
* 日本語
* Norsk (bokmål)
* Norsk (nynorsk)
* Nouormand
* Novial
* Occitan
* O'zbek
* پښتو
* ភាសាខ្មែរ
* Plattdüütsch
* Polski
* Português
* Română
* Runa Simi
* Русский
* Gagana Samoa
* संस्कृत
* Sardu
* Scots
* Sesotho
* Shqip
* Sicilianu
* Simple English
* Slovenčina
* Slovenščina
* Српски / Srpski
* Srpskohrvatski / Српскохрватски
* Suomi
* Svenska
* Tagalog
* தமிழ்
* Taqbaylit
* తెలుగు
* ไทย
* Tiếng Việt
* Тоҷикӣ/tojikī
* ᏣᎳᎩ
* Türkçe
* Українська
* Vèneto
* Võro
* Walon
* Winaray
* Wolof
* ייִדיש
* Yorùbá
* 粵語
* Zeêuws
* Žemaitėška
* 中文
Powered by MediaWiki
Wikimedia Foundation
* This page was last modified on 15 July 2008, at 16:17.
* All text is available under the terms of the GNU Free
Contents
[hide]
* 1 Definition of music
* 2 History
o 2.1 Ancient
o 2.2 Medieval and Renaissance Europe
o 2.3 European Baroque
o 2.4 European Classical
o 2.5 Romantic
o 2.6 20th century
* 3 Performance
o 3.1 Aural tradition
o 3.2 Ornamentation
* 4 Production
o 4.1 Composition
o 4.2 Notation
o 4.3 Improvisation
o 4.4 Theory
* 5 Cognition
* 6 Sociology
* 7 Media and technology
o 7.1 Internet
* 8 Business
* 9 Education
o 9.1 Primary
o 9.2 Academia
o 9.3 Ethnomusicology
* 10 Music therapy
* 11 See also
* 12 References
* 13 Further reading
* 14 External links
Definition of music
See also: Music genre
Musical notations
Musical notations
Greek philosophers and ancient Indians defined music as tones ordered horizontally as melodies and vertically as harmonies. Music theory, within this realm, is studied with the presupposition that music is orderly and often pleasant to hear. However, in the 20th century, composers challenged the notion that music had to be pleasant by creating music that explored harsher, darker timbres. The existence of some modern-day music genres such as death metal and grindcore, which enjoy an extensive underground following, indicate that even the harshest sounds can be considered music if the listener is so inclined.
20th-century composer John Cage disagreed with the notion that music must consist of pleasant, discernible melodies. Instead, he argued that any sounds we can hear can be music, saying, for example, "There is no noise, only sound."[2] According to musicologist Jean-Jacques Nattiez, "the border between music and noise is always culturally defined—which implies that, even within a single society, this border does not always pass through the same place; in short, there is rarely a consensus.… By all accounts there is no single and intercultural universal concept defining what music might be, except that it is 'sound through time'."[3]
The creation, performance, significance, and even the definition of music vary according to culture and social context. Music ranges from strictly organized compositions (and their recreation in performance), through improvisational music to aleatoric forms. Music can be divided into genres and subgenres, although the dividing lines and relationships between music genres are often subtle, sometimes open to individual interpretation, and occasionally controversial. Within "the arts", music can be classified as a performing art, a fine art, or an auditory art form.
History
Figurines playing stringed instruments, excavated at Susa, 2nd millennium BC. Iran National Museum.
Figurines playing stringed instruments, excavated at Susa, 2nd millennium BC. Iran National Museum.
Main article: History of music
The development of music among humans must have taken place against the backdrop of natural sounds such as birdsong and the sounds other animals use to communicate.[citation needed] Prehistoric music is the name which is given to all music produced in preliterate cultures.[citation needed][4]
Ancient
Globe icon
The examples and perspective in this article or section may not represent a worldwide view of the subject.
Please improve this article or discuss the issue on the talk page.
Main article: Ancient music
A range of paleolithic sites have yielded bones in which lateral holes have been pierced: these are usually identified as flutes,[5] blown at one end like the Japanese shakuhachi. The earliest written records of musical expression are to be found in the Samaveda of India and in 4,000 year old cuneiform from Ur.[citation needed] Instruments, such as the seven-holed flute and various types of stringed instruments have been recovered from the Indus Valley Civilization archaeological sites.[6] India has one of the oldest musical traditions in the world—references to Indian classical music (marga) can be found in the ancient scriptures of the Hindu tradition, the Vedas. The traditional art or court music of China has a history stretching for more than three thousand years. Music was an important part of cultural and social life in Ancient Greece: mixed-gender choruses performed for entertainment, celebration and spiritual ceremonies; musicians and singers had a prominent role in ancient Greek theater
In the 9th century, al-Farabi wrote a notable book on music titled Kitab al-Musiqi al-Kabir ("Great Book of Music"). He played and invented a variety of musical instruments and devised the Arab tone system of pitch organisation, which is still used in Arabic music.[7]
Medieval and Renaissance Europe
Main articles: Medieval music and Renaissance music
While musical life in Europe was undoubtedly rich in the early Medieval era, as attested by artistic depictions of instruments, writings about music, and other records, the only European repertory which has survived from before about 800 is the monophonic liturgical plainsong of the Roman Catholic Church, the central tradition of which was called Gregorian chant. Several schools of liturgical polyphony flourished beginning in the 12th century. Alongside these traditions of sacred music, a vibrant tradition of secular song developed, exemplified by the music of the troubadours, trouvères and Minnesänger.
Much of the surviving music of 14th century Europe is secular. By the middle of the 15th century, composers and singers used a smooth polyphony for sacred musical compositions such as the mass, the motet, and the laude, and secular forms such as the chanson and the madrigal. The introduction of commercial printing had an immense influence on the dissemination of musical styles.[citation needed]
European Baroque
Main article: Baroque music
The first operas, written around 1600 and the rise of contrapuntal music define the end of the Renaissance and the beginning of the Baroque era that lasted until roughly 1750, the year of the death of Johann Sebastian Bach.
Allegory of Music, by Filippino Lippi
Allegory of Music, by Filippino Lippi
Allegory of Music on the Opéra Garnier
Allegory of Music on the Opéra Garnier
German Baroque composers wrote for small ensembles including strings, brass, and woodwinds, as well as choirs, pipe organ, harpsichord, and clavichord. During the Baroque period, several major music forms were defined that lasted into later periods when they were expanded and evolved further, including the fugue, the invention, the sonata, and the concerto.[8]
European Classical
Main article: Classical period (music)
The music of the Classical period is characterized by homophonic texture, often featuring a prominent melody with accompaniment. These new melodies tended to be almost voice-like and singable. The now popular instrumental music was dominated by further evolution of musical forms initially defined in the Baroque period: the sonata, and the concerto, with the addition of the new form, the symphony. Joseph Haydn and Wolfgang Amadeus Mozart, well known even today, are among the central figures of the Classical period.
Romantic
Main article: Romantic music
Ludwig van Beethoven and Franz Schubert were transitional composers, leading into the Romantic period, with their expansion of existing genres, forms, and functions of music. In the Romantic period, the emotional and expressive qualities of music came to take precedence over the orientation towards technique and tradition. The late 19th century saw a dramatic expansion in the size of the orchestra, and in the role of concerts as part of urban society. Later Romantic composers created complex and often much longer musical works, merging and expanding traditional forms that had previously been used separately. For example, counterpoint, combined with harmonic structures to create more extended chords with increased use of dissonance and to create dramatic tension and resolution.
20th century
Main article: 20th century music
In the 20th century there was a vast increase in music listening as the radio gained popularity worldwide and new media and technologies were developed to record, capture, reproduce and distribute music. The focus of art music was characterized by exploration. Claude Debussy has become well-known and respected for his orientation towards colors and depictions in his compositional style. Igor Stravinsky, Arnold Schoenberg, and John Cage were all influential composers in 20th century art music. Jazz evolved and became a significant genre of music over the course of the 20th century, and during the second half of that century, rock music and hip hop music did the same.
Performance
Main article: Performance
Chinese Naxi musicians
Chinese Naxi musicians
Performance is the physical expression of music. Often, a musical work is performed once its structure and instrumentation are satisfactory to its creators; however, as it gets performed, it can evolve and change.
A performance can either be rehearsed or improvised. Improvisation is a musical idea created on the spot (such as a guitar solo or a drum solo), with no prior premeditation, while rehearsal is vigorous repetition of an idea until it has achieved cohesion. Musicians will generally add improvisation to a well-rehearsed idea to create a unique performance.
Many cultures include strong traditions of solo and performance, such as in Indian classical music, and in the Western Art music tradition. Other cultures, such as in Bali, include strong traditions of group performance. All cultures include a mixture of both, and performance may range from improvised solo playing for one's enjoyment to highly planned and organised performance rituals such as the modern classical concert, religious processions, music festivals or music competitions.
Chamber music, which is music for a small ensemble with only a few of each type of instrument, is often seen as more intimate than symphonic works. A performer may be referred to as a musician.
Aural tradition
Many types of music, such as traditional blues and folk music were originally preserved in the memory of performers, and the songs were handed down orally, or aurally (by ear). When the composer of music is no longer known, this music is often classified as "traditional". Different musical traditions have different attitudes towards how and where to make changes to the original source material, from quite strict, to those which demand improvisation or modification to the music. A culture's history may also be passed by ear through song.
Ornamentation
Main article: Ornament (music)
The detail included explicitly in the music notation varies between genres and historical periods. In general, art music notation from the 17th through the 19th century required performers to have a great deal of contextual knowledge about performing styles.
For example, in the 17th and 18th century, music notated for solo performers typically indicated a simple, unornamented melody. However, it was expected that performers would know how to add stylistically-appropriate ornaments such as trills and turns. In the 19th century, art music for solo performers may give a general instruction such as to perform the music expressively, without describing in detail how the performer should do this. It was expected that the performer would know how to use tempo changes, accentuation, and pauses (among other devices) to obtain this "expressive" performance style. In the 20th century, art music notation often became more explicit and used a range of markings and annotations to indicate to performers how they should play or sing the piece.
In popular music and jazz, music notation almost always indicates only the basic framework of the melody, harmony, or performance approach; musicians and singers are expected to know the performance conventions and styles associated with specific genres and pieces. For example, the "lead sheet" for a jazz tune may only indicate the melody and the chord changes. The performers in the jazz ensemble are expected to know how to "flesh out" this basic structure by adding ornaments, improvised music, and chordal accompaniment.
Production
Main article: Music production
Music is composed and performed for many purposes, ranging from aesthetic pleasure, religious or ceremonial purposes, or as an entertainment product for the marketplace. Amateur musicians compose and perform music for their own pleasure, and they do not derive their income from music. Professional musicians are employed by a range of institutions and organisations, including armed forces, churches and synagogues, symphony orchestras, broadcasting or film production companies, and music schools. Professional musicians sometimes work as freelancers, seeking contracts and engagements in a variety of settings.
There are often many links between amateur and professional musicians. Beginning amateur musicians take lessons with professional musicians. In community settings, advanced amateur musicians perform with professional musicians in a variety of ensembles and orchestras. In some cases, amateur musicians attain a professional level of competence, and they are able to perform in professional performance settings.
A distinction is often made between music performed for the benefit of a live audience and music that is performed for the purpose of being recorded and distributed through the music retail system or the broadcasting system. However, there are also many cases where a live performance in front of an audience is recorded and distributed (or broadcast).
Composition
Main article: Musical composition
"Composition" is often classed as the creation and recording of music via a medium by which others can interpret it (i.e. paper or sound). Many cultures use at least part of the concept of preconceiving musical material, or composition, as held in western classical music. Even when music is notated precisely, there are still many decisions that a performer has to make. The process of a performer deciding how to perform music that has been previously composed and notated is termed interpretation.
Different performers' interpretations of the same music can vary widely. Composers and song writers who present their own music are interpreting, just as much as those who perform the music of others or folk music. The standard body of choices and techniques present at a given time and a given place is referred to as performance practice, where as interpretation is generally used to mean either individual choices of a performer, or an aspect of music which is not clear, and therefore has a "standard" interpretation.
In some musical genres, such as jazz and blues, even more freedom is given to the performer to engage in improvisation on a basic melodic, harmonic, or rhythmic framework. The greatest latitude is given to the performer in a style of performing called free improvisation, which is material that is spontaneously "thought of" (imagined) while being performed, not preconceived. According to the analysis of Georgiana Costescu,[citation needed] improvised music usually follows stylistic or genre conventions and even "fully composed" includes some freely chosen material. Composition does not always mean the use of notation, or the known sole authorship of one individual.
Music can also be determined by describing a "process" which may create musical sounds; examples of this range from wind chimes, through computer programs which select sounds. Music which contains elements selected by chance is called Aleatoric music, and is associated with such composers as John Cage, Morton Feldman, and Witold Lutosławski.
Musical composition is a term that describes the composition of a piece of music. Methods of composition vary widely from one composer to another, however in analysing music all forms — spontaneous, trained, or untrained — are built from elements comprising a musical piece. Music can be composed for repeated performance or it can be improvised: composed on the spot. The music can be performed entirely from memory, from a written system of musical notation, or some combination of both. Study of composition has traditionally been dominated by examination of methods and practice of Western classical music, but the definition of composition is broad enough to include spontaneously improvised works like those of free jazz performers and African drummers such as the Ewe drummers.
What is important in understanding the composition of a piece is singling out its elements. An understanding of music's formal elements can be helpful in deciphering exactly how a piece is constructed. A universal element of music is how sounds occur in time, which is referred to as the rhythm of a piece of music.
When a piece appears to have a changing time-feel, it is considered to be in rubato time, an Italian expression that indicates that the tempo of the piece changes to suit the expressive intent of the performer. Even random placement of random sounds, which occurs in musical montage, occurs within some kind of time, and thus employs time as a musical element.
Notation
Main article: Musical notation
Notation is the written expression of music notes and rhythms on paper using symbols. When music is written down, the pitches and rhythm of the music is notated, along with instructions on how to perform the music. The study of how to read notation involves music theory, harmony, the study of performance practice, and in some cases an understanding of historical performance methods.
Written notation varies with style and period of music. In Western Art music, the most common types of written notation are scores, which include all the music parts of an ensemble piece, and parts, which are the music notation for the individual performers or singers. In popular music, jazz, and blues, the standard musical notation is the lead sheet, which notates the melody, chords, lyrics (if it is a vocal piece), and structure of the music. Scores and parts are also used in popular music and jazz, particularly in large ensembles such as jazz "big bands."
In popular music, guitarists and electric bass players often read music notated in tablature, which indicates the location of the notes to be played on the instrument using a diagram of the guitar or bass fingerboard. Tabulature was also used in the Baroque era to notate music for the lute, a stringed, fretted instrument.
Notated music is produced as sheet music. To perform music from notation requires an understanding of both the musical style and the performance practice that is associated with a piece of music or genre.
Improvisation
Main article: Musical improvisation
Improvisation is the creation of spontaneous music. Improvisation is often considered an act of instantaneous composition by composers, where compositional techniques are employed with or without preparation.
Theory
Main article: Music theory
Music theory encompasses the nature and mechanics of music. It often involves identifying patterns that govern composers' techniques. In a more detailed sense, music theory (in the western system) also distills and analyzes the elements of music – rhythm, harmony (harmonic function), melody, structure, and texture. People who study these properties are known as music theorists.
Cognition
Further information: Hearing (sense) and Psychoacoustics
Concert in the Mozarteum, Salzburg
Concert in the Mozarteum, Salzburg
The field of music cognition involves the study of many aspects of music including how it is processed by listeners. Rather than accepting the standard practices of analyzing, composing, and performing music as a given, much research in music cognition seeks instead to uncover the mental processes that underlie these practices. Also, research in the field seeks to uncover commonalities between the musical traditions of disparate cultures and possible cognitive "constraints" that limit these musical systems. Questions regarding musical innateness, and emotional responses to music are also major areas of research in the field.
Deaf people can experience music by feeling the vibrations in their body, a process which can be enhanced if the individual holds a resonant, hollow object. A well-known deaf musician is the composer Ludwig van Beethoven, who composed many famous works even after he had completely lost his hearing. Recent examples of deaf musicians include Evelyn Glennie, a highly acclaimed percussionist who has been deaf since age twelve, and Chris Buck, a virtuoso violinist who has lost his hearing. This is relevant because it indicates that music is a deeper cognitive process than unexamined phrases such as, "pleasing to the ear" would suggest. Much research in music cognition seeks to uncover these complex mental processes involved in listening to music, which may seem intuitively simple, yet are vastly intricate and complex.
Sociology
Half-section of the Song Dynasty (960–1279) version of Night Revels of Han Xizai, original by Gu Hongzhong; the painting shows musicians entertaining guests in a 10th century household. In the center are three female musicians playing guan, two female musicians playing transverse bamboo flutes, and a male musician playing a wooden clapper called paiban.
Half-section of the Song Dynasty (960–1279) version of Night Revels of Han Xizai, original by Gu Hongzhong; the painting shows musicians entertaining guests in a 10th century household. In the center are three female musicians playing guan, two female musicians playing transverse bamboo flutes, and a male musician playing a wooden clapper called paiban.
Music is experienced by individuals in a range of social settings ranging from being alone to attending a large concert. Musical performances take different forms in different cultures and socioeconomic milieus. In Europe and North America, there is often a divide between what types of music are viewed as a "high culture" and "low culture." "High culture" types of music typically include Western art music such as Baroque, Classical, Romantic, and modern-era symphonies, concertos, and solo works, and are typically heard in formal concerts in concert halls and churches, with the audience sitting quietly in seats.
Other types of music - including, but not limited to, jazz, blues, soul, and country - are often performed in bars, nightclubs, and theatres, where the audience may be able to drink, dance, and express themselves by cheering. Until the later 20th century, the division between "high" and "low" musical forms was widely accepted as a valid distinction that separated out better quality, more advanced "art music" from the popular styles of music heard in bars and dance halls.
However, in the 1980s and 1990s, musicologists studying this perceived divide between "high" and "low" musical genres argued that this distinction is not based on the musical value or quality of the different types of music.[citation needed] Rather, they argued that this distinction was based largely on the socioeconomic standing or social class of the performers or audience of the different types of music.[citation needed] For example, whereas the audience for Classical symphony concerts typically have above-average incomes, the audience for a rap concert in an inner-city area may have below-average incomes. Even though the performers, audience, or venue where non-"art" music is performed may have a lower socioeconomic status, the music that is performed, such as blues, rap, punk, funk, or ska may be very complex and sophisticated.
When composers introduce styles of music which break with convention, there can be a strong resistance from academic music experts and popular culture. Late-period Beethoven string quartets, Stravinsky ballet scores, serialism, bebop-era jazz, hip hop, punk rock, and electronica have all been considered non-music by some critics when they were first introduced.[citation needed]
Such themes are examined in the sociology of music. The sociological study of music, sometimes called sociomusicology, is often pursued in departments of sociology, media studies, or music, and is closely related to the field of ethnomusicology.
Media and technology
Further information: Computer music
The music that composers make can be heard through several media; the most traditional way is to hear it live, in the presence, or as one of the musicians. Live music can also be broadcast over the radio, television or the Internet. Some musical styles focus on producing a sound for a performance, while others focus on producing a recording which mixes together sounds which were never played "live". Recording, even of styles which are essentially live, often uses the ability to edit and splice to produce recordings which are considered better than the actual performance.
As talking pictures emerged in the early 20th century, with their prerecorded musical tracks, an increasing number of moviehouse orchestra musicians found themselves out of work.[9] During the 1920s live musical performances by orchestras, pianists, and theater organists were common at first-run theaters.[10] With the coming of the talking motion pictures, those featured performances were largely eliminated. The American Federation of Musicians (AFM) took out newspaper advertisements protesting the replacement of live musicians with mechanical playing devices. One 1929 ad that appeared in the Pittsburgh Press features an image of a can labeled "Canned Music / Big Noise Brand / Guaranteed to Produce No Intellectual or Emotional Reaction Whatever"[11]
Since legislation introduced to help protect performers, composers, publishers and producers, including the Audio Home Recording Act of 1992 in the United States, and the 1979 revised Berne Convention for the Protection of Literary and Artistic Works in the United Kingdom, recordings and live performances have also become more accessible through computers, devices and Internet in a form that is commonly known as Music-On-Demand.
In many cultures, there is less distinction between performing and listening to music, since virtually everyone is involved in some sort of musical activity, often communal. In industrialized countries, listening to music through a recorded form, such as sound recording or watching a music video, became more common than experiencing live performance, roughly in the middle of the 20th century.
Sometimes, live performances incorporate prerecorded sounds. For example, a disc jockey uses disc records for scratching, and some 20th century works have a solo for an instrument or voice that is performed along with music that is prerecorded onto a tape. Computers and many keyboards can be programmed to produce and play Musical Instrument Digital Interface (MIDI) music. Audiences can also become performers by participating in karaoke, an activity of Japanese origin which centres around a device that plays voice-eliminated versions of well-known songs. Most karaoke machines also have video screens that show lyrics to songs being performed; performers can follow the lyrics as they sing over the instrumental tracks.
Internet
The advent of the Internet has transformed the experience of music, partly through the increased ease of access to music and the increased choice. Chris Anderson, in his book The Long Tail: Why the Future of Business is Selling Less of More, suggests that while the economic model of supply and demand describes scarcity, the Internet retail model is based on abundance. Digital storage costs are low, so a company can afford to make its whole inventory available online, giving customers as much choice as possible. It has thus become economically viable to offer products that very few people are interested in. Consumers' growing awareness of their increased choice results in a closer association between listening tastes and social identity, and the creation of thousands of niche markets.[12]
Another effect of the Internet arises with online communities like YouTube and MySpace. MySpace has made social networking with other musicians easier, and greatly facilitates the distribution of one's music. YouTube also has a large community of both amateur and professional musicians who post videos and comments.[citation needed] Professional musicians also use YouTube as a free publisher of promotional material.
YouTube users, for example, no longer only download and listen to MP3s, but also actively create their own. According to Don Tapscott and Anthony D. Williams, in their book Wikinomics, there has been a shift from a traditional consumer role to what they call a "prosumer" role, a consumer who both creates and consumes. Manifestations of this in music include the production of mashes, remixes, and music videos by fans.[13]
Business
Main article: Music industry
The music industry refers to the business industry connected with the creation and sale of music. It consists of record companies, labels and publishers that distribute recorded music products internationally and that often control the rights to those products. Some music labels are "independent," while others are subsidiaries of larger corporate entities or international media groups.
Education
Primary
Main article: Music education
The incorporation of music training from preschool to post secondary education is common in North America and Europe. Involvement in music is thought to teach basic skills such as concentration, counting, listening, and cooperation while also promoting understanding of language, improving the ability to recall information, and creating an environment more conducive to learning in other areas.[14] In elementary schools, children often learn to play instruments such as the recorder, sing in small choirs, and learn about the history of Western art music. In secondary schools students may have the opportunity to perform some type of musical ensembles, such as choirs, marching bands, concert bands, jazz bands, or orchestras, and in some school systems, music classes may be available. Some students also take private music lessons with a teacher. Amateur musicians typically take lessons to learn musical rudiments and beginner- to intermediate-level musical techniques.
At the university level, students in most arts and humanities programs can receive credit for taking music courses, which typically take the form of an overview course on the history of music, or a music appreciation course that focuses on listening to music and learning about different musical styles. In addition, most North American and European universities have some type of musical ensembles that non-music students are able to participate in, such as choirs, marching bands, or orchestras. The study of Western art music is increasingly common outside of North America and Europe, such as the Indonesian Institute of the Arts in Yogyakarta, Indonesia, or the classical music programs that are available in Asian countries such as South Korea, Japan, and China. At the same time, Western universities and colleges are widening their curriculum to include music of non-Western cultures, such as the music of Africa or Bali (e.g. Gamelan music).
Academia
Musicology is the study of the subject of music. The earliest definitions defined three sub-disciplines: systematic musicology, historical musicology, and comparative musicology or ethnomusicology. In contemporary scholarship, one is more likely to encounter a division of the discipline into music theory, music history, and ethnomusicology. Research in musicology has often been enriched by cross-disciplinary work, for example in the field of psychoacoustics. The study of music of non-western cultures, and the cultural study of music, is called ethnomusicology.
Graduates of undergraduate music programs can go on to further study in music graduate programs. Graduate degrees include the Master of Music, the Master of Arts, the Doctor of Philosophy (PhD) (e.g., in musicology or music theory), and more recently, the Doctor of Musical Arts, or DMA. The Master of Music degree, which takes one to two years to complete, is typically awarded to students studying the performance of an instrument, education, voice or composition. The Master of Arts degree, which takes one to two years to complete and often requires a thesis, is typically awarded to students studying musicology, music history, or music theory. Undergraduate university degrees in music, including the Bachelor of Music, the Bachelor of Music Education, and the Bachelor of Arts (with a major in music) typically take three to five years to complete. These degrees provide students with a grounding in music theory and music history, and many students also study an instrument or learn singing technique as part of their program.
The PhD, which is required for students who want to work as university professors in musicology, music history, or music theory, takes three to five years of study after the Master's degree, during which time the student will complete advanced courses and undertake research for a dissertation. The DMAis a relatively new degree that was created to provide a credential for professional performers or composers that want to work as university professors in musical performance or composition. The DMA takes three to five years after a Master's degree, and includes advanced courses, projects, and performances. In Medieval times, the study of music was one of the Quadrivium of the seven Liberal Arts and considered vital to higher learning. Within the quantitative Quadrivium, music, or more accurately harmonics, was the study of rational proportions.
Zoomusicology is the study of the music of non-human animals, or the musical aspects of sounds produced by non-human animals. As George Herzog (1941) asked, "do animals have music?" François-Bernard Mâche's Musique, mythe, nature, ou les Dauphins d'Arion (1983), a study of "ornitho-musicology" using a technique of Nicolas Ruwet's Language, musique, poésie (1972) paradigmatic segmentation analysis, shows that bird songs are organised according to a repetition-transformation principle. Jean-Jacques Nattiez (1990), argues that "in the last analysis, it is a human being who decides what is and is not musical, even when the sound is not of human origin. If we acknowledge that sound is not organised and conceptualised (that is, made to form music) merely by its producer, but by the mind that perceives it, then music is uniquely human."
Music theory is the study of music, generally in a highly technical manner outside of other disciplines. More broadly it refers to any study of music, usually related in some form with compositional concerns, and may include mathematics, physics, and anthropology. What is most commonly taught in beginning music theory classes are guidelines to write in the style of the common practice period, or tonal music. Theory, even that which studies music of the common practice period, may take many other forms. Musical set theory is the application of mathematical set theory to music, first applied to atonal music. Speculative music theory, contrasted with analytic music theory, is devoted to the analysis and synthesis of music materials, for example tuning systems, generally as preparation for composition.
Ethnomusicology
Main article: Ethnomusicology
In the West, much of the history of music that is taught deals with the Western civilization's art music. The history of music in other cultures ("world music" or the field of "ethnomusicology") is also taught in Western universities. This includes the documented classical traditions of Asian countries outside the influence of Western Europe, as well as the folk or indigenous music of various other cultures.
Popular styles of music varied widely from culture to culture, and from period to period. Different cultures emphasised different instruments, or techniques, or uses for music. Music has been used not only for entertainment, for ceremonies, and for practical and artistic communication, but also for propaganda in totalitarian countries.
There is a host of music classifications, many of which are caught up in the argument over the definition of music. Among the largest of these is the division between classical music (or "art" music), and popular music (or commercial music - including rock and roll, country music, and pop music). Some genres don't fit neatly into one of these "big two" classifications, (such as folk music, world music, or jazz music).
As world cultures have come into greater contact, their indigenous musical styles have often merged into new styles. For example, the United States bluegrass style contains elements from Anglo-Irish, Scottish, Irish, German and African instrumental and vocal traditions, which were able to fuse in the United States' multi-ethnic society. Genres of music are determined as much by tradition and presentation as by the actual music. Some works, like George Gershwin's Rhapsody in Blue, are claimed by both jazz and classical music. Many current music festivals celebrate a particular musical genre.
Indian music, for example, is one of the oldest and longest living types of music, and is still widely heard and performed in South Asia, as well as internationally (especially since the 1960s). Indian music has mainly 3 forms of classical music, Hindustani, Carnatic, and Dhrupad styles. It has also a large repertoire of styles, which involve only percussion music such as the talavadya performances famous in South India.
Music therapy
Main article: Music therapy
Robert Burton wrote in his 17th century work, The Anatomy of Melancholy, that music and dance were critical in treating mental illness, especially melancholia.[15] He said that
But to leave all declamatory speeches in praise of divine music, I will confine myself to my proper subject: besides that excellent power it hath to expel many other diseases, it is a sovereign remedy against despair and melancholy, and will drive away the devil himself.
Burton noted that
...Canus, a Rhodian fiddler, in Philostratus, when Apollonius was inquisitive to know what he could do with his pipe, told him, "That he would make a melancholy man merry, and him that was merry much merrier than before, a lover more enamoured, a religious man more devout."
[16][17][18]
In November 2006, Dr. Michael J. Crawford[19] and his colleagues also found that music therapy helped schizophrenic patients.[20] In the Ottoman Empire, mental illnesses were treated with music.[21]
See also
Music portal
* List of basic music topics
* List of music topics
References
1. ^ Mousike, Henry George Liddell, Robert Scott, A Greek-English Lexicon, at Perseus
2. ^ John Cage, 79, a Minimalist Enchanted With Sound, Dies
3. ^ Nattiez 1990: 47-8, 55
4. ^ "Primitive music" is an obsolescent term for prehistoric music.[citation needed]
5. ^ Son et musique au paléolithique", Pour La Science,. 253, 52-58 (1998)
6. ^ The Music of India By Reginald MASSEY, Jamila MASSEY. Google Books
7. ^ Touma (1996), p.170
8. ^ Baroque Music by Elaine Thornburgh and Jack Logan, Ph. D.
9. ^ American Federation of Musicians/History
10. ^ Hubbard (1985), p. 429.
11. ^ "Canned Music on Trial" part of Duke University's Ad*Access project.
12. ^ Anderson, Chris (2006). The Long Tail: Why the Future of Business is Selling Less of More. Hyperion. ISBN 1-4013-0237-8.
13. ^ Tapscott, Don; Williams, Anthony D. (2006-12-28). Wikinomics: How Mass Collaboration Changes Everything. Portfolio Hardcover. ISBN 978-1591841388.
14. ^ Woodall and Ziembroski, 2002
15. ^ cf. The Anatomy of Melancholy, Robert Burton, subsection 3, on and after line 3,480, "Music a Remedy"
16. ^ Ismenias the Theban, Chiron the centaur, is said to have cured this and many other diseases by music alone: as now thy do those, saith Bodine, that are troubled with St. Vitus's Bedlam dance. Project Gutenberg's The Anatomy of Melancholy, by Democritus Junior
17. ^ "Humanities are the Hormones: A Tarantella Comes to Newfoundland. What should we do about it?" by Dr. John Crellin, MUNMED, newsletter of the Faculty of Medicine, Memorial University of Newfoundland, 1996.
18. ^ Aung, Steven K.H., Lee, Mathew H.M., "Music, Sounds, Medicine, and Meditation: An Integrative Approach to the Healing Arts", Alternative & Complementary Therapies, Oct 2004, Vol. 10, No. 5: 266-270.
19. ^ Dr. Michael J. Crawford page at Imperial College London, Faculty of Medicine, Department of Psychological Medicine.
20. ^ Crawford, Mike J.; Talwar, Nakul, et al. (November 2006). "Music therapy for in-patients with schizophrenia: Exploratory randomised controlled trial". The British Journal of Psychiatry (2006) 189: 405–409. doi:10.1192/bjp.bp.105.015073. PMID 17077429.
21. ^ Treatment of Mental Illnesses With Music Therapy - A different approach from history
Further reading
* Harwood, Dane (1976). "Universals in Music: A Perspective from Cognitive Psychology", Ethnomusicology 20, no. 3:521-33.
* Johnson, Julian (2002). Who Needs Classical Music?: Cultural Choice and Musical Value. Oxford University Press. ISBN 0-19-514681-6.
* Kertz-Welzel, Alexandra. "Piano Improvisation Develops Musicianship." Orff-Echo XXXVII No. 1 (2004): 11-14.
* Kertz-Welzel, Alexandra. "The Singing Muse: Three Centuries of Music Education in Germany." Journal of Historical Research in Music Education XXVI no. 1 (2004): 8-27.
* Kertz-Welzel, Alexandra. "Didaktik of Music: A German Concept and its Comparison to American Music Pedagogy." International Journal of Music Education (Practice) 22 No. 3 (2004): 277-286.
* Kertz-Welzel, Alexandra. "General Music Education in Germany Today: A Look at How Popular Music is Engaging Students." General Music Today 18 no. 2 (Winter 2005): 14-16.
* Molino, Jean (1975). "Fait musical et sémiologue de la musique", Musique en Jeu, no. 17:37-62.
* Nattiez, Jean-Jacques (1987). Music and Discourse: Toward a Semiology of Music (Musicologie générale et sémiologue, 1987). Translated by Carolyn Abbate (1979). ISBN 0-691-02714-5.
* Owen, Harold (2000). Music Theory Resource Book. Oxford University Press. ISBN 0-19-511539-2.
* Small, Christopher (1977). Music, Society, Education. John Calder Publishers, London. ISBN 0-7145-3614-8
* Habib Hassan Touma (1996). The Music of the Arabs, trans. Laurie Schwartz. Portland, Oregon: Amadeus Press. ISBN 0-931340-88-8
* Woodall, Laura and Brenda Ziembroski, (2002). Literacy Through Music.
External links
Find more about Music on Wikipedia's sister projects:
Dictionary definitions
Textbooks
Quotations
Source texts
Images and media
News stories
Learning resources
* BBC Blast Music For 13-19 year olds interested in learning about, making, performing and talking about music.
* The Virginia Tech Multimedia Music Dictionary, with definitions, pronunciations, examples, quizzes and simulations
* The Music-Web Music Encyclopedia, for musicians, composers and music lovers
* Dolmetsch free online music dictionary, complete, with references to a list of specialised music dictionaries (by continent, by instrument, by genre, etc.)
* "On Hermeneutical Ethics and Education: Bach als Erzieher", a paper by Prof. Miguel Ángel Quintana Paz in which he explains the history of the different views hold about music in Western societies, since the Ancient Greece to our days.
* Monthly Online Features From Bloomingdale School of Music, addressing a variety of musical topics for a wide audience
* Arts and Music Uplifting Society towards Transformation and Tolerance Articles meant to stimulate people’s awareness about the peace enhancing, transforming, communicative, educational and healing powers of music.
Retrieved from "http://en.wikipedia.org/wiki/Music"
Categories: Music | Sound | Greek loanwords
Hidden categories: All articles with unsourced statements | Articles with unsourced statements since November 2007 | Semi-protected against vandalism | Articles with limited geographic scope | Europe-centric | Articles with unsourced statements since March 2008 | Articles with unsourced statements since May 2007
Views
* Article
* Discussion
* View source
* History
Personal tools
* Log in / create account
Navigation
* Main Page
* Contents
* Featured content
* Current events
* Random article
Search
Interaction
* About Wikipedia
* Community portal
* Recent changes
* Contact Wikipedia
* Donate to Wikipedia
* Help
Toolbox
* What links here
* Related changes
* Upload file
* Special pages
* Printable version
* Permanent link
* Cite this page
Languages
* Afrikaans
* አማርኛ
* العربية
* Aragonés
* ܐܪܡܝܐ
* Asturianu
* Avañe'ẽ
* Bamanankan
* বাংলা
* Bân-lâm-gú
* Basa Banyumasan
* Беларуская
* Беларуская (тарашкевіца)
* Boarisch
* Bosanski
* Brezhoneg
* Български
* Català
* Чăвашла
* Cebuano
* Česky
* Corsu
* Cymraeg
* Dansk
* Deutsch
* ދިވެހިބަސް
* Eesti
* Ελληνικά
* Español
* Esperanto
* Euskara
* فارسی
* Føroyskt
* Français
* Frysk
* Furlan
* Gaeilge
* Gàidhlig
* Galego
* Hak-kâ-fa
* 한국어
* हिन्दी
* Hrvatski
* Ido
* Bahasa Indonesia
* Interlingua
* Interlingue
* Иронау
* Íslenska
* Italiano
* עברית
* Basa Jawa
* ಕನ್ನಡ
* ქართული
* कश्मीरी - (كشميري)
* Kernewek
* Кыргызча
* Kreyòl ayisyen
* Ladino
* ລາວ
* Latina
* Latviešu
* Lëtzebuergesch
* Lietuvių
* Líguru
* Limburgs
* Lojban
* Magyar
* മലയാളം
* Malti
* मराठी
* مَزِروني
* Bahasa Melayu
* Nahuatl
* Nederlands
* Nedersaksisch
* नेपाली
* 日本語
* Norsk (bokmål)
* Norsk (nynorsk)
* Nouormand
* Novial
* Occitan
* O'zbek
* پښتو
* ភាសាខ្មែរ
* Plattdüütsch
* Polski
* Português
* Română
* Runa Simi
* Русский
* Gagana Samoa
* संस्कृत
* Sardu
* Scots
* Sesotho
* Shqip
* Sicilianu
* Simple English
* Slovenčina
* Slovenščina
* Српски / Srpski
* Srpskohrvatski / Српскохрватски
* Suomi
* Svenska
* Tagalog
* தமிழ்
* Taqbaylit
* తెలుగు
* ไทย
* Tiếng Việt
* Тоҷикӣ/tojikī
* ᏣᎳᎩ
* Türkçe
* Українська
* Vèneto
* Võro
* Walon
* Winaray
* Wolof
* ייִדיש
* Yorùbá
* 粵語
* Zeêuws
* Žemaitėška
* 中文
Powered by MediaWiki
Wikimedia Foundation
* This page was last modified on 15 July 2008, at 16:17.
* All text is available under the terms of the GNU Free
Subscribe to:
Posts (Atom)
