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computer, device capable of performing a series of arithmetic or logical operations. A computer is distinguished from a calculating machine, such as an electronic calculator, by being able to store a computer program (so that it can repeat its operations and make logical decisions), by the number and complexity of the operations it can perform, and by its ability to process, store, and retrieve data without human intervention. Computers developed along two separate engineering paths, producing two distinct types of computer—analog and digital. An analog computer operates on continuously varying data; a digital computer performs operations on discrete data.
Computers are categorized by both size and the number of people who can use them concurrently. Supercomputers are sophisticated machines designed to perform complex calculations at maximum speed; they are used to model very large dynamic systems, such as weather patterns. Mainframes, the largest and most powerful general-purpose systems, are designed to meet the computing needs of a large organization by serving hundreds of computer terminals at the same time. Minicomputers, though somewhat smaller, also are multiuser computers, intended to meet the needs of a small company by serving up to a hundred terminals. Microcomputers, computers powered by a microprocessor, are subdivided into personal computers and workstations, the latter typically incorporating RISC processors. Although microcomputers were originally single-user computers, the distinction between them and minicomputers has blurred as microprocessors have become more powerful. Linking multiple microcomputers together through a local area network or joining multiple microprocessors together in a parallel-processing system has enabled smaller systems to perform tasks once reserved for mainframes, and the techniques of grid computing have enabled computer scientists to utilize the unemployed processing power of computers connected over a network or the Internet.
Advances in the technology of integrated circuits have spurred the development of smaller and more powerful general-purpose digital computers. Not only has this reduced the size of the large, multi-user mainframe computers—which in their early years were large enough to walk through—to that of pieces of furniture, but it has also made possible powerful, single-user personal computers and workstations that can sit on a desktop or be easily carried. These, because of their relatively low cost and versatility, have replaced typewriters in the workplace and rendered the analog computer inefficient. The reduced size of computer components has also led to the development of thin, lightweight notebook computers and even smaller computer tablets and smartphones that have much more computing and storage capacity than that of the desktop computers that were available in the early 1990s.
Processing of Data
Storage and Retrieval of Data
Associated with the CPU is the main storage, or memory, where results or other data are stored for periods of time ranging from a small fraction of a second to days or weeks before being retrieved for further processing. Once made up of vacuum tubes and later of small doughnut-shaped ferromagnetic cores strung on a wire matrix, main storage now consists of integrated circuits, each of may contain billions of semiconductor devices. Where each vacuum tube or core represented one bit and the total memory of the computer was measured in thousands of bytes (or kilobytes, KB), modern computer memory chips represent hundreds of millions of bytes (or megabytes, MB) and the total memory of both personal and mainframe computers is measured in billions of bytes (gigabytes, GB) or more. Read-only memory (ROM), which cannot be written to, maintains its content at all times and is used to store the computer's control information. Random-access memory (RAM), which both can be read from and written to, is lost each time the computer is turned off. Modern computers now include cache memory, which the CPU can access faster than RAM but slower than the registers; data in cache memory also is lost when the computer is turned off.
Programs and data that are not currently being used in main storage can be saved on auxiliary or secondary storage. Although punched paper tape and punched cards once served this purpose, the major materials used today are magnetic tape and disks and flash memory devices, all of which can be read from and written to, and two types of optical disks, the compact disc (CD) and its successor the digital versatile disc (DVD). When compared to RAM, these are less expensive (though flash memory is more expensive than the other two), are not volatile (i.e., data is not lost when the power to the computer is shut off), and can provide a convenient way to transfer data from one computer to another. Thus operating instructions or data output from one computer can be stored and be used later either by the same computer or another.
In a system using magnetic tape the information is stored by a specially designed tape recorder somewhat similar to one used for recording sound. Magnetic tape is now largely used for offsite storage of large volumes of data or major systems backups. In magnetic and optical disk systems the principle is the same; the magnetic or optical medium lies in a path, or track, on the surface of a disk. The disk drive also contains a motor to spin the disk and a magnetic or optical head or heads to read and write the data to the disk. Drives take several forms, the most significant difference being whether the disk can be removed from the drive assembly. Flash memory devices, such as USB flash drives, flash memory cards, and solid-state drives, use nonvolatile memory that can be erased and reprogrammed in blocks.
Removable magnetic disks made of mylar enclosed in a plastic holder (older versions had paper holders) are now largely outdated. These floppy disks have varying capacities, with very high density disks holding 250 MB—more than enough to contain a dozen books the size of Tolstoy's Anna Karenina. Internal and external magnetic hard disks, or hard drives, are made of metal and arranged in spaced layers. They can hold vastly more data than floppies or optical disks, and can read and write data much faster than floppies. As hard disks dropped in price, they became increasingly included as a component of personal computers and replaced floppy disks as the standard media for the storage of operating systems, programs, and data.
Compact discs can hold hundreds of megabytes, and have been used, for example, to store the information contained in an entire multivolume encyclopedia or set of reference works. DVD is an improved optical storage technology capable of storing as much as ten times the data that CD technology can store. CD–Read-Only Memory (CD-ROM) and DVD–Read-Only Memory (DVD-ROM) disks can only be read—the disks are impressed with data at the factory but once written cannot be erased and rewritten with new data. The latter part of the 1990s saw the introduction of new optical storage technologies: CD-Recordable (CD-R) and DVD-Recordable (DVD-R, DVD+R), optical disks that can be written to by the computer to create a CD-ROM or DVD-ROM, but can be written to only once; and CD-ReWritable (CD-RW), DVD-ReWritable (DVD-RW and DVD+RW), and DVD–Random Access Memory (DVD-RAM), disks that can be written to multiple times.
Flash memory devices, a still more recent development, are an outgrowth of electrically erasible programmable read-only memory. Although more expensive than magnetic and optical storage technologies, flash memory can be read and written to much faster, permitting shorter boot times and quicker data access and storage. Because flash memory also is resistant to mechanical shock and has become increasingly compact, a USB flash drive allows for the easy, portable external storage of large quantities of data. Solid-state drives are more easily accessed and written to than magnetic hard drives and use less power, and have become common in high-end, lightweight notebook computers and in high-performance computers. Flash memory is also used in computer tablets and smartphones. Hybrid drives, which combine a smaller amount of flash memory with a large magnetic hard drive, permit the economical storage of large amounts of data while benefitting from a more responsive access to frequently used but only occasionally changed operating system and program files.
Data are entered into the computer and the processed data made available via input/output devices, also called peripherals. All auxiliary storage devices are used as input/output devices. For many years, the most popular input/output medium was the punched card. The most popular input devices are the computer terminal and internal magnetic hard drives, and the most popular output devices are the computer display screen associated with a terminal (typically displaying output that has been processed by a graphics processing unit) and the printer. Human beings can directly communicate with the computer through computer terminals, entering instructions and data by means of keyboards much like the ones on typewriters, by using a pointing device such as a mouse, trackball, or touchpad, or by speaking into a microphone that is connected to computer running voice-recognition software. The result of the input may be displayed on a liquid-crystal, light-emitting diode, or cathode-ray tube screen or on printer output. Another important input/output device in modern computers is the network card, which allows the computer to connect to a computer network and the Internet using a wired or radio (wireless) connection. The CPU, main storage, auxiliary storage, and input/output devices collectively make up a cumputer system.
Sharing the Computer's Resources
Generally, the slowest operations that a computer must perform are those of transferring data, particularly when data is received from or delivered to a human being. The computer's central processor is idle for much of this period, and so two similar techniques are used to use its power more fully.
Time sharing, used on large computers, allows several users at different terminals to use a single computer at the same time. The computer performs part of a task for one user, then suspends that task to do part of another for another user, and so on. Each user only has the computer's use for a fraction of the time, but the task switching is so rapid that most users are not aware of it. Most of the tens of millions of computers in the world are stand-alone, single-user devices known variously as personal computers or workstations. For them, multitasking involves the same type of switching, but for a single user. This permits a user, for example, to have one file printed and another uploaded to an Internet website while editing a third in a word-processing session and listening to a recording streamed over the Internet. Personal computers can also be linked together in a network, where each computer is connected to others, usually by network, coaxial, or fiber-optic cable or by radio signals (wireless), permitting all to share resources such as printers, hard-disk storage devices, and an Internet connection. Cloud computing is another form of resource sharing. Delivering access to both hardware and software over a network, most often the Internet, cloud computing is designed to allow many individuals and organizations using a wide range of devices both ease of access to computing resources and flexibility in changing the type and volume of the resources to which they have access.
Computer Programs and Programming Languages
Before a computer can be used for a given purpose, it must first be programmed, that is, prepared for use by loading a set of instructions, or program. The various programs by which a computer controls aspects of its operations, such as those for translating data from one form to another, are known as software, as contrasted with hardware, which is the physical equipment comprising the installation. In most computers the moment-to-moment control of the machine resides in a special software program called an operating system, or supervisor. Other forms of software include assemblers and compilers for programming languages and applications for business and home use (see computer program). Software is of great importance; the usefulness of a highly sophisticated array of hardware can be limited by the lack of adequate software.
Each instruction in the program may be a simple, single step, telling the computer to perform some arithmetic operation, to read the data from some given location in the memory, to compare two numbers, or to take some other action. The program is entered into the computer's memory exactly as if it were data, and on activation, the machine is directed to treat this material in the memory as instructions. Other data may then be read in and the computer can carry out the program to complete the particular task.
Since computers are designed to operate with binary numbers, all data and instructions must be represented in this form; the machine language, in which the computer operates internally, consists of the various binary codes that define instructions together with the formats in which the instructions are written. Since it is time-consuming and tedious for a programmer to work in actual machine language, a programming language, or high-level language, designed for the programmer's convenience, is used for the writing of most programs. The computer is programmed to translate this high-level language into machine language and then solve the original problem for which the program was written. Many high-level programming languages are now universal, varying little from machine to machine.
Development of Computers
Although the development of digital computers is rooted in the abacus and early mechanical calculating devices, Charles Babbage is credited with the design of the first modern computer, the “analytical engine,” during the 1830s. Vannevar Bush built a mechanically operated device, called a differential analyzer, in 1930; it was the first general-purpose analog computer. John Atanasoff constructed the first electronic digital computing device in 1939; a full-scale version of the prototype was completed in 1942 at Iowa State College (now Iowa State Univ.). In 1943 Conrad Zuse built the Z3, a fully operational electromechanical computer.
During World War II, the Colossus was developed for British codebreakers; it was the first programmable electronic digital computer. The Mark I, or Automatic Sequence Controlled Calculator, completed in 1944 at Harvard by Howard Aiken, was the first machine to execute long calculations automatically, while the first all-purpose electronic digital computer, ENIAC (Electronic Numerical Integrator And Calculator), which used thousands of vacuum tubes, was completed in 1946 at the Univ. of Pennsylvania. UNIVAC (UNIVersal Automatic Computer) became (1951) the first computer to handle both numeric and alphabetic data with equal facility; intended for business and government use, this was the first widely sold commercial computer.
First-generation computers were supplanted by the transistorized computers (see transistor) of the late 1950s and early 60s, second-generation machines that were smaller, used less power, and could perform a million operations per second. They, in turn, were replaced by the third-generation integrated-circuit machines of the mid-1960s and 1970s that were even smaller and were far more reliable. The 1970s, 80s, and 90s were characterized by the development of the microprocessor and the evolution of increasingly smaller but powerful computers, such as the personal computer and personal digital assistant (PDA), which ushered in a period of rapid growth in the computer industry.
The World Wide Web was unveiled in 1990, and with the development of graphical web browser programs in succeeding years the Web and the Internet spurred the growth of general purpose home computing and the use of computing devices as a means of social interaction. Smartphones, which integrate a range of computer software with a cellular telephone that now typically has a touchscreen interface, date to 2000 when a PDA was combined with a cellphone. Although computer tablets date to the 1990s, they only succeeded commercially in 2010 with the introduction of Apple's iPad, which built on software developed for smartphones. The increasing screen size on some smartphones has made them the equivalent of smaller computer tablets, leading some to call them phablets.
See S. G. Nash, A History of Scientific Computing (1990); D. I. A. Cohen, Introduction to Computer Theory (2d ed. 1996); P. Norton, Peter Norton's Introduction to Computers (2d ed. 1996); A. W. Biermann, Great Ideas in Computer Science: A Gentle Introduction (2d ed. 1997); R. L. Oakman, The Computer Triangle: Hardware, Software, People (2d ed. 1997); R. Maran, Computers Simplified (4th ed. 1998); A. S. Tanenbaum and J. R. Goodman. Structured Computer Organization (4th ed. 1998).
a device or set of devices for the mechanization and automation of data processing (computations).
Modern computers are subdivided into three classes according to the method of representing data: (1) analog computers, in which data are represented in the form of continuously changing variables expressed by physical quantities (the angle of rotation of a shaft, the intensity of an electrical current, voltage, and so on); (2) digital computers, in which data are represented in the form of discrete values of variables (numbers) expressed by a combination of discrete values of some physical quantity; and (3) hybrid computers, various units of which represent data by one or the other method.
Historically, digital computing devices appeared first—for example, abacuses and their numerous precursors. In the 17th century the French scientist B. Pascal, and later the German mathematician G. W. von Leibniz, built the first digital computers. The first computer suitable for practical use was Thomas de Colmar’s adding machine (1820). V. T. Odhner’s adding machine, which became very widespread, was built in 1874. In the early 20th century tabulators appeared for performing various statistical, bookkeeping, and financial-banking operations.
The idea of building a general-purpose digital computer belongs to Professor C. Babbage of Cambridge University. In 1833 he designed a computer whose features are close to those of modern devices. The plan was ahead of the needs of the day and technical possibilities for realization.
The development of the theory of relay-switching circuits and experience in using telephone and punched card equipment made it possible during the 1930’s to undertake the development of a computer with program control. At first electromagnetic relays were used. The first such machine, the Mark I, was built in 1944 in the United States. The first electronic digital computer, the ENIAC (Electronic Numerical Integrator and Computer) was built in 1946, also in the United States.
In the Soviet Union, the MESM (Small Electronic Calculator) electronic digital computer was developed in 1950 at the Academy of Sciences of the Ukrainian SSR under the direction of Academician S. A. Lebedev. The MESM marked the beginning of work in the field of mathematical electronic machine building in the USSR. In subsequent years a number of digital computers that differed in productivity and technical concept were built in the USSR to satisfy the needs of the national economy (for example, the BESM, Strela, M-20, M-220, Minsk, Ural, and Mir).
The first continuous-operation devices appeared in the 16th and 17th centuries. These include the slide rule and nomograms for navigational calculations. In the mid-19th century, very simple mechanical integrators appeared. Work on analog computers developed significantly at the turn of the 20th century. Machines for solving differential equations, electromechanical integrating machines, and others were developed. In the USSR, the beginning of analog computer development dates back to 1927; it is associated with the work of S. A. Gershgorin, M. V. Kirpichev, I. S. Bruk, V. S. Luk’ianov, and others. During the 1950’s and 1960’s, several types of analog computers were built, many of which have found wide application.
The development of electronic computers is closely linked to achievements in the field of electronics. The first electronic computers used vacuum tubes; it is customary to call these computers first-generation machines. The development of semiconductor radio electronics made possible the transition to designing second- and third-generation computers. They are characterized by a more complex logic diagram and by software, which is a programmed extension of the hard-ware. The technology for manufacturing second-generation computers differed little from that used for the manufacture of first-generation computers; vacuum tubes were replaced by semiconductor triodes (transistors) and diodes. Third-generation computers are built with integrated circuits, which contain dozens of transistors, resistors, and diodes in a single module. The transition to producing computers with integrated circuits demanded an almost complete revision of the technology of production of electronic computers.
The theory of mathematical modeling is the basis for constructing analog computers. Using analogies among phenomena that differ in their physical nature, the analog computer models the processes being calculated. A large part of the analog computer equipment consists of linear and non-linear decision elements. In electronic analog computers these are operational DC amplifiers (integrator, amplifier, inverter), units of coefficients, typical nonlinearities, delays, and so on. To solve a specific problem, the units of an analog computer are interconnected in the necessary combinations. Output data of the analog computer are obtained from readings on the displays at the terminal points of the circuit. The analog computer is characterized by high speed of operation, simplicity in the linkage with the object being investigated, the possibility of easily changing the parameters of the problem under investigation both during its preparation and during the solution process, comparatively low precision, and a limited class of solvable problems.
Solving a problem on digital computers involves the sequential performance of arithmetic operations on numbers that correspond to quantities representing the initial data. The numbers are usually represented in the form of an aggre-gate of mechanical, pneumatic, or electrical pulses and are fixed by elements that can each assume several stable states that correspond strictly to one digit of the number. Before solution on the digital computer, the problem is broken down into a series of simple sequential operations and their order is set—that is, a program of computations is drawn up.
Digital computers are subdivided into three classes according to their method of control: those with manual control, those with a rigid program; and general-purpose types. Digital computers with manual control include keyboard computers, adding machines, and lever-operated computers. Modern desk digital computers are manufactured almost entirely with electronic components. The computing process is controlled manually, which results in low computation speed. The digital computer with manual control is a means of mechanizing calculation operations and is only suitable for solving very simple problems with a limited number of computations.
Rigid-program digital computers include tabulators, specialized machines oriented to solving a narrow range of problems (for example, on-board computers), and so on. In these computers the computing process is controlled automatically by a program set up on a switchboard or permanently built into the machine. The digital computer with a switchable program is a means for partial automation of the computing process and is rapidly being replaced by general-purpose digital computers. Computers with built-in programs are used in cases where simplicity, reliability, low cost, and small size and weight are needed, primarily for one-time use (for example, in missiles).
General-purpose computers with automatic program control are the most refined means of automating the labor-consuming processes of human mental activity. Modern general-purpose digital computers are a complicated automatic computing complex that includes a processor, an immediate-access memory, one or several large-capacity external memories, and data input-output units. The process of computation is controlled by the control device and the pro-gram of computations located in the computer memory. The loading of particular units, the coordination of their operation, and the control of the sequence of solving problems are done by program equipment. The set of programs that per-forms these and many other functions is called software. Algorithmic languages (ALGOL, FORTRAN, COBOL, and others) are used to describe problem-solving. The input of initial data and programs and the output of results in the form most convenient for the user are accomplished by the set of input-output devices that are part of the general-purpose digital computer. Initial data may be given in the form of graphs, digital and textual documents, images of the object being calculated (for example, an overall view of a building, a cross section of an airplane wing, and so on), audiovisual display, and others.
Digital computers are characterized by high productivity and precision in the results obtained and by algorithmic universality, which results from the fact that the rearrangement of the digital computer to solve a new problem involves only a change in the computation program and the initial data stored in the computer memory, without changing the design of the machine itself.
Hybrid computer systems consist of organically linked analog and digital computers. Data exchange between analog-action and discrete-action computers is accomplished through special convertors. A division of functions between machines is typical for a combined system: the analog computer is used to reproduce fast-occurring processes with limited precision of variables, and the digital computer is used for computations with greater precision and for statistical processing of results. The hybrid computing system combines high precision and speed, which are more difficult to obtain by means of just one of the computers.
A. N. MIAMLIN
the term adopted in foreign literature (chiefly English-language) for equipment that operates automatically either according to a preassigned program or according to sequential instructions to solve mathematical problems and problems of economics, statistics, production planning, management, and so forth. The term usually refers to electronic computers (in Russian, elektronnye vychislitel’nye mashiny).
What does it mean when you dream about a computer?
For someone who works in front of a computer every day, this could simply be a reflection of daily life in a dream. A computer can also indicate research, analysis, or communication, depending on how one uses a computer. We sometimes say that something doesn’t “compute” as a way of saying we don’t understand, so a broken computer in a dream could represent confusion.
A device that receives, processes, and presents information. The two basic types of computers are analog and digital. Although generally not regarded as such, the most prevalent computer is the simple mechanical analog computer, in which gears, levers, ratchets, and pawls perform mathematical operations—for example, the speedometer and the watt-hour meter (used to measure accumulated electrical usage). The general public has become much more aware of the digital computer with the rapid proliferation of the hand-held calculator and a large variety of intelligent devices and especially with exposure to the Internet and the World Wide Web. See Internet
An analog computer uses inputs that are proportional to the instantaneous value of variable quantities, combines these inputs in a predetermined way, and produces outputs that are a continuously varying function of the inputs and the processing. These outputs are then displayed or connected to another device to cause action, as in the case of a speed governor or other control device. Small electronic analog computers are frequently used as components in control systems. If the analog computer is built solely for one purpose, it is termed a special-purpose electronic analog computer. In any analog computer the key concepts involve special versus general-purpose computer designs, and the technology utilized to construct the computer itself, mechanical or electronic. See Analog computer
In contrast, a digital computer uses symbolic representations of its variables. The arithmetic unit is constructed to follow the rules of one (or more) number systems. Further, the digital computer uses individual discrete states to represent the digits of the number system chosen. A digital computer can easily store and manipulate numbers, letters, images, sounds, or graphical information represented by a symbolic code. Through the use of the stored program, the digital computer achieves a degree of flexibility unequaled by any other computing or data-processing device.
The advent of the relatively inexpensive and readily available personal computer, and the combination of the computer and communications, such as by the use of networks, have dramatically expanded computer applications. The most common application now is probably text and word processing, followed by electronic mail. See Electronic mail, Local-area networks, Microcomputer
Computers have begun to meet the barrier imposed by the speed of light in achieving higher speeds. This has led to research and development in the areas of parallel computers (in order to accomplish more in parallel rather than by serial computation) and distributed computers (taking advantage of network connections to spread the work around, thus achieving more parallelism). Continuing demand for more processing power has led to significant changes in computer hardware and software architectures, both to increase the speed of basic operations and to reduce the overall processing time. See Computer systems architecture, Concurrent processing, Distributed systems (computers), Multiprocessing, Supercomputer
The physical components from which a computer is constructed (electronic circuits and input/output devices) are known as "hardware". Most computers have four types of hardware component: CPU, input, output and memory. The CPU (central processing unit) executes programs ("software") which tell the computer what to do. Input and output (I/O) devices allow the computer to communicate with the user and the outside world. There are several kinds of memory - fast, expensive, short term memory (e.g. RAM) to hold intermediate results, and slower, cheaper, long-term memory (e.g. magnetic disk and magnetic tape) to hold programs and data between jobs.
See also analogue computer.
computerA computer is a general-purpose machine that processes data according to a set of instructions temporarily stored internally. The computer and all the equipment attached to it are "hardware." The instructions that tell the computer what to do are "software."
The software that controls the computer is called an "operating system," and the software that inputs, processes and outputs data for the user is called a "program," "application" or "app." See operating system, application, how to select a computer, stored program concept and computer generations.
RAM vs. Storage
The interplay between temporary memory (the RAM) and permanent storage is how computers work. The instructions (software) are first written into RAM, and the computer executes them to input, process and output the data.
RAM is a temporary workspace, while storage is permanent and comprises any hard drive, solid state drive (SSD), optical disc or USB drive on the same computer or another computer in the network. After processing the data internally, the computer can send a copy of the results from RAM back to storage, to a printer or to another computer. The more RAM, the more programs and data the computer can work with quickly, and entry-level computers generally have at least 4GB (four gigabytes) of RAM. The more storage, the more data can be saved. Entry-level computers typically have at least 512GB of disk or 128GB of SSD storage.
Storage can only be read and written in large blocks called "sectors" that hold hundreds or thousands of bytes. However, it is the RAM that allows one or more bytes to be manipulated independently. This "single byte addressability" is why data are brought into RAM for processing. See RAM and storage vs. memory.
For a basic explanation of how the computer processes data, see 3 C's.
|The UNIVAC I (Frankfurt Germany, 1956)|
|Imagine being here watching this UNIVAC CPU being pushed up the ramp and someone says "you know some day all of that will fit on the head of a pin." See UNIVAC I.|
|How About the Tip of a Pencil?|
|In fact, these PICmicro microcontrollers from Microchip (www.microchip.com), are a whole lot faster than the UNIVAC I. See microcontroller.|
|Ordenador and Ordinateur|
|In Spain and France, a computer is an "organizer." The word is surely less intimidating than "computer," and in fact, computers do as much if not more organizing and rearranging than they do deriving mathematical results.|