The computer is a general-purpose device that can be programmed to perform a set of arithmetic or logic operations.Possibility series such operations be changed allowing the computer to be used for solving various tasks. Usually the purpose of these operations is the processing of entries (data) represented in digital (digital) form, the result of which can be displayed in a usable form.From a functional point of view, all computers are made up of four main components: the arithmetic logic unit which performs arithmetic and logical operations; control unit that can change the order of execution of operations based on the recorded information; memory in which is stored the input, output and any intermediate data; and input-output devices through which data entering and leaving the computer. In practice in most modern computers arithmetic logic unit, control unit and part of the memory are united in a common component called CPU.Computers can have different device as a purely mechanical structures have been known since ancient times, but almost all modern computers are electronic. The first fully electronic computers were created in the middle of the XX century, the earliest of which are the size of a large room with electric power exceeding 150 kW. Modern machines based on integrated circuits are millions to billions of times higher performance in power from a few dozen to several hundred watts.   Today, some simple computers are compact enough to fit in various mobile devices and economical enough to be powered by a small battery.In everyday speech the term "computer" is most often understood PCs in their various forms, which nowadays have become a symbol of the information age. At the same time, far more numerous embedded computers are part of a variety of devices - from MP3 players to fighter aircraft and from toys to industrial robots.NameIn Bulgarian language, once computers are also called computing machine.In English, the earliest known use of the word "computer" (in English: computer, literally "scorers") is a book from 1613 "The yong mans gleanings" the English writer Richard Braithwaite. There it is called the person performing the calculations, as this remains the basic meaning of the word until the mid 20th century. From the late 19th century it began to be used in matters similar to today - a machine that carries out computations. In Bulgarian language, especially in the specialized technical literature, computers initially called "electronic computers" or "digital computing machines" (often abbreviated EIM and TSEIM). Subsequently spread borrowed from English "computer."HistoryForerunners of the electronic computerComputer The modern appearance resulting from the combined use of the two technologies. They in turn develop independently for many years - the automated calculation and programmability. The first means of automated calculation - cream - still appear in ancient times. are known from Sumer in the middle of the third millennium BC In the I and II century BCmechanical devices are designed for astronomical and navigational calculations - widely used Astrolabe and rare and complex mechanism of Antikythera. At the beginning of XVII century was invented slide rules, which remains widely used in massive introduction of electronic calculators in the XX century.In 1642 the Frenchman Blaise Pascal creates a mechanical calculator. Remains the same and many godinim, the only such facility to perform calculations. In 1851 the Frenchman Charles Xavier Thomas de Colmar first demonstrate its simplified prototype arithmometer. Same becomes the first mass-produced calculator, because it turns out that it is sufficiently robust for everyday office use. The emergence of a market for mechanical calculators and the desire to create a more powerful and flexible devices played an important role in the emergence of the first computers, stimulating research Englishman Charles Babbage. Development of calculators and computers remains connected and later, when in the middle of the XX century the development of cheaper electronic calculators led to the creation of the microprocessor became the basis of computer technology over the next decades.Before the advent of computers, there are different programmable mechanical devices such as mechanical toys and music boxes. Back in I century Egyptian engineer Heron construct all mechanical theater powered by a complex system of ropes that performs continuous 10 minutes performance. In 1801 the Frenchman Joseph Marie Jacquart make improvements in the loom, creating a system of punch cards, through which can be programmed intricate patterns automatically woven into the fabric.First electronic computersThe first computers, such as ENIAC, need a physical change in the binding of components to perform various actions, which is why computers are called fixed program. Since the concept of a central processor is typically coupled with the possibility of execution of various computer programs earliest devices which can be so called the first computer with the stored program.The concept of a programmable computer has existed in draft John Presper Eckert and John Mauchly of ENIAC, but was abandoned to allow the machine to be completed faster. On June 30, 1945, before the completion of ENIAC, the mathematician John von Neumann published a study entitled "First draft of a report on EDVAC" ("First Draft of a Report on the EDVAC"), which describes the principles of a computer with a stored program to be completed in August 1949.  EDVAC was designed to perform a number of different instructions that can be combined to form useful programs.The most important innovation in EDVAC is that the programs are stored in high-speed memory, rather than being determined by way of a physical connection to the computer components. Thus overcome the most severe limitation of ENIAC - the considerable time and effort required to reconfigure the computer to perform a new task. In Von Neumann computer program can be changed only by changing the contents of the computer memory. Even before the completion of the EDVAC, ENIAC was reconstructed in a way that allows it to also store programs.Although usually credited with creating a computer program stored is attributed to John von Neumann, and others before him, such as Konrad Zuse, have been proposed and implemented such ideas. System Mark I, completed before EDVAC, also uses the stored programs, but recorded on paper punched tape rather than electronic memory. The main difference between the EDVAC Mark I and in that at Mark I storing and processing of data and instructions is divided, while in the system of Von Neumann, and in most modern processors, they use the same memory.As a digital device, the processor is reduced to a set of discrete states and needs some kind of switching elements to differentiate and change these conditions. Before the widespread use of transistors for this purpose are usually used relays and tubes. While these devices are much faster than the earlier mechanical switches, for various reasons, they are not very reliable. For example, construction of DC circuits with sequential logic relays requires additional hardware to eliminate the problems with the contact jumps. Tubes at this problem does not exist, but they must be heated before being fully fit for use and time stop working because of pollution their cathodes that occurs as a result of their normal way of working, while depressurize the lamp quickly accelerates. A problem with a lamp whole processor must be diagnosed to locate and replace the damaged lamp.With these reasons early electronic (tube) computers were generally faster but less reliable than electromechanical (using relays) machines. Tube computers like EDVAC, work an average of 8-10 hours between failures, whereas relay systems implemented on printsioa of Mark I, very rarely fail.Ultimately tube processors become more widespread, as significantly higher speed proved more important than reliability problems.Most of these early synchronous processors operate at a low clock speed compared to current microelectronic devices.During this period, the normal system clock frequencies are 100 kHz to 4 MHz, the main limiting factor remains the switching speed devices.Discrete transistors and integrated circuits
CPU, memory and external bus DEC PDP-8 / I., built with ICsDrives in computers is complicated after various new technologies facilitate the creation of smaller and more reliable electronic devices. The first such invention is the transistor. In the 50s and 60s based transistors processors no longer rely on bulky, unreliable and precarious switching elements such as tubes and relays. This enables the construction of more complex and reliable CPUs consist of one or more printed circuit boards containing discrete components.During this period, distributes a new method for the production of a large number of transistors in a limited space. IC allows multiple transistors to engage in a common semiconductor socket called chip. Initially, the integrated circuits are used only for a very simple non-specialized circuits, such as for individual logic elements. Processors based on such simple integrated circuits, commonly called devices with low integration (SSI). SSI integrated circuits used in computers such as the Apollo Guidance Computer, typically comprise several tens of transistors. Building a whole processor SSI ICs required thousands of individual chips, but still takes a lot less space and has low power consumption from previous devices with discrete transistors. With advances in microelectronics, integrated circuits began to include more and more transistors, reducing the number of individual schemes needed to create a complete processor. Integrated circuits with medium (MSI) and strong integration (LSI) have already hundreds, then thousands of transistors. Thus, the first computer with a DEC LSI device version of the model PDP-11 processor has only four ICs.In 1964 IBM introduced the PC architecture System/360, which was first introduced the idea of microcode and standardization of programs executed by a processor. Until then, most electronic computers, including those from the same manufacturer are incompatible and can not run the same programs. System/360 architecture became so popular that for decades dominated the market for mainframe computers.Transistors based computers have several distinct advantages over their predecessors. Besides the improved reliability and lower power consumption, they have a much higher rate due to the short time of switching transistor in comparison with tubes and relay. Thanks to the increased reliability and substantially higher speed switching elements in 60s processors reach clock speeds of tens of megahertz.During this period appeared the first high-performance vector processors, early precursors of later specialized supercomputers.PCsThe advent of microprocessors in the 70s significantly altered the structure and use of computers. After arrival on the market of the first microprocessor (Intel 4004) in 1970 and the first model, spread widely (Intel 8080) in 1974, this group of processors shifted almost entirely other species. The main producers of mainframe computers and minicomputers start own work to improve its previous computer architecture, microprocessors, and create a set of instructions that are compatible with those used in older systems, their hardware and software. This process is coupled with the emergence and massively successful personal computers.While older processor models are composed of individual components and numerous small integrated circuits located on one or more circuit boards, microprocessors consist of a very small number of ICs, usually only one. The smaller total CPU represents a single chip, allowing even greater reduction of switching time. This allows synchronous microprocessors reach clock speeds of tens of megahertz to several gigahertz.Moreover, the increase in the ability to construct ever smaller transistors in integrated circuits is highly increased complexity and number of transistors in a separate processor. This empirical regularity is formulated in the observed from the 60s to today Moore's Law, which states that technically achievable density of transistors on integrated circuits doubles for 18 to 24 months.Despite the complexity, size, structure and general appearance of processors vary significantly from their appearance here, the basic principles of their functioning remain approximately the same. Almost all modern processors can be accurately described as Von Neumann machines with stored program. Although Moore's Law is still in force in recent years raises the question of limitations in the technology of integrated circuits. The final miniaturization of the NAND gates increases the impact of physical phenomena, such as elektromigratsiyata which can interfere with this process. This is one reason to look for new designs of processors as the quantum computer, and to expand the applications of parallelism and other methods that expand the classical model of Von Neumann.Classification of computers
Classification by purpose
Supercomputer - extremely fast machineMini supercomputerCluster - multiple separate machines running under the management of a specialized program combining their powerMainframe computer - designed for centralized processing of large datasets and simultaneous operation of more than 100 usersBusiness ServerMinicomputer - a multiuser machine, capable of supporting simultaneous operation of 10 or more usersWorkstation - a specialized powerful computerPC - normally used for operations performed by one personDesktop PCVirtual PC - Webtop 2.0 - fully virtualized PC running kernelLaptopPDAController - highly specialized to perform a specific activity, usually embedded in a more complex deviceThis classification is rather vague in nature. This is because constantly discovering new uses for computers. What few decades ago it was impossible for the PC, can now be part of the daily life of home users. Therefore, the boundaries between the above terms is unclear and varies with time.Classification according to technological performance
Technology for the production of computers have changed much from their original creation. The first computers were entirely mechanical. In the 30s of XX century introduced the use of relays, and in the 40s John Atanasov and Clifford Berry created the first electronic computer (ABC). From the 60s until now computers are fully transistor. Besides these core technologies in the development of computers has had experience with other quite exotic ones. For example, for economic modeling have been used with various narrowing channel through which water flows.Today, developing new technologies to increase the performance of computers. Here are the main ones:Optical computerQuantum computerClassification is so important technology of production, as the example, the functions it performs computer. The only exception quantum computers as their technology would allow so to increase the speed of processing information that will lead to qualitatively new features of the computer.Applications
The first electronic computers were very expensive and large - the size of a room.This restricted their use to scientific calculations, often for military purposes. ENIAC example has been created for the ballistic calculations, but the later is used to check the structure of the hydrogen bomb.
Random access memory