A computer is a machine Informatique. It is a whole of electronic circuits making it possible to handle data in binary format, or bits; This machine makes it possible to treat Information S according to sequences of preset instructions or program S. It interacts with the environment thanks to Périphérique S (screen, Clavier, Modem…).
See also: History of data processing
The word computer was introduced by IBM France in 1955. François Girard, then responsible for the service publicity of the company, had the idea to consult his former professor of letters in Paris, Jacques Perret, in order to ask him to propose a word characterizing best possible than one called a calculator vulgarly (literal translation of the English word “computer”). This last proposed “computer”, a word fallen in disuse in the past indicating a Ordonnateur, even the concept of order ecclesiastical in the Catholic church (processing). Let us note that the professor suggested “electronic ordinatrice more precisely”, the female one having been able to allow, according to him, to better distinguish the religious use of the countable use of the word…
The first computer functioning in binary language was the Colossus, conceived at the time of the 2nd world war. At the end of the war, it was dismounted and hidden because of its strategic importance. The ENIAC , its American counterpart created in 1945, was thus regarded during several years as the first computer, before the existence of growing old Colossus was revealed.
General informationThe computers were initially used for the Calcul (of integers initially, then floating).
- One cannot however compare them to simple Calculateur S: indeed, the result of the treatment of a computer can be not only one series of numbers, but also a new program (usable by this computer or by another).
- In the architecture of von Neumann, the data are standardized and can be interpreted indifferently like logical numbers, instructions, values or any arbitrarily defined symbol (letter of the alphabet, for example).
calculation represents a possible applications. In this case, the data are treated like numbers.
- the computer is also used for its possibilities of organization of information , inter alia on peripheral of magnetic storage. One calculated at the end of the Années 1980 that without the computers one would need all the French population just to do in this country the only work of the Banque S.
This creation of a neologism was at the origin of multiple translations of the expressions Supercomputer , supercomputer or supercomputer, and Quantum computer , quantum calculator or quantum computer. In this last case, the use of the word " ordinateur" is precisely overrated because the possible possibilities for quantum calculation are far from the versatility of a " ordinateur".
The experiment learned how to distinguish in a computer two aspects, whose second had been with the underestimated departure:
- physical, material architecture (alias Hardware or hardware );
- architecture Software it (alias Software or software ); a very technically advanced computer for its time as the Gamma 60 of the company Bull did not have awaited success, for the simple reason that there existed little of means of implementing its technical possibilities conveniently. Software - and its complement the services (formation, maintenance, etc) - form since the medium of the Years 1980 main part of the costs of data-processing equipment, the minority material having only one share there.
The computers could be sensitive to the Bombe EMP.
Operation of a computer
The Technical S used to manufacture these machines changed enormously since the Années 1940 and became a Technologie (i.e. an industrial unit organized around techniques) with whole share since the Seventies. Many still uses the Concept S defined by John von Neumann, although this architecture is in regression: the programs hardly any more change themselves (what would be regarded as a bad practice of programming), and the material takes into account this news gives by separating today clearly storage from the instructions and the data, including in the mask S.
The Architecture of von Neumann broke up the computer into four distinct parts
- the arithmetic logic unit (UAL) or treatment unit: its role is to carry out the basic operations, a little as a calculator would do it.
- the control unit . It is the equivalent of the fingers which would actuate the calculator.
- the memory which contain at the same time the data and the program which will say to the control unit which calculations to make on these data. The memory divides between volatile memory (programs and given in the course of operation) and permanent memory (source programs and data of the machine).
- the input-outputs : devices which make it possible to communicate with the outside world.
UAL and CPU
The arithmetic logic unit or UAL is the element which carries out the elementary operations (additions, subtractions, etc), the logical operators (AND, OR, Ni, etc) and the operations of comparison (for example the comparison of equality between two storage areas). In fact the UAL carries out the calculations computer.
The control unit takes its instructions in the memory. Those state to him that it must order with the UAL and, how it will have to possibly act according to the results that this one will provide him. Once the finished operation, the control unit master key either to the following instruction, or with another instruction to which the program orders to him to connect.
The control unit facilitates the communication between the arithmetic logic unit, the memory as well as the peripherals. It manages the majority of the execution of the instructions in the computer.
Within the system, the memory can be described like a succession of numbered cells containing each one an minor amount of information. This information can be used to indicate to the computer what it must do (Instruction S) or contain data to be treated. In the majority of the architectures, it is the same memory which is used for the two functions. In the calculators massively parallel, one even admits that program instructions are substituted for others in the course of operation when that results in a greater effectiveness. This practice was formerly current, but the requirements of legibility of the software Génie have made it regress, except in this particular case, for several decades.
This memory can be récrite as much of time than necessary. Size of each memory stack, as well as technology used varied according to the costs and the needs: 8 bits for telecommunications, 12 bits for instrumentation (DEC) and 60 bits for large scientific calculators (Control Dated). A consensus ended up being carried out around the Octet like addressable unit, and of instructions on format of 4 or 8 bytes.
In all the cases of figure, the Octet remains addressable, which simplifies the writing of the programs.
The techniques used for the realization of the memories included/understood electromechanical relays, tubes with mercury in which were generated acoustic waves, individual Transistor S, Tore S of Ferrite, and finally of the Integrated circuits including million transistors.
The devices of input/output make it possible the computer to communicate with outside. The number of these devices is very important, of the keyboard to the screen.
The common point between all the peripheral of entry is that they convert the information which they recover of outside in comprehensible data by the computer. Contrary, the peripherals of exit decode the furnished information by the computer in order to make it usable by the user.
These various parts are connected by three drunk, the adress bus, the data bus and the bus of order. A bus is a grouping of a certain number of electric wires carrying out a connection to transport binary data coded on several bits.
- the Bus of address transports the addresses generated by the U.C.T. (Central processing unit of Treatment) to select a box memory or an internal register of the one of the blocks. The number of bits conveyed by this bus depends on the quantity of memory which must be addressed.
- the Data bus transports the data exchanged between the various elements of the system.
- the Control bus transmits the various signals of synchronization necessary to the operation of the system: signal of reading (RD), signal of writing (WR), signal of selection (CS: Chip Select).
The miniaturization makes it possible to integrate the UAL and the control unit within same a Integrated circuit known under the name of Microprocesseur.
- Typically, the memory is located on integrated circuits close to the processor, part of this memory, the Mémoire hiding place, being able to be located on the same integrated circuit as the UAL.
- the unit remains on the majority of architectures supplemented of a clock which gives rhythm the processor. Of course, it is wished that it be fastest possible, but one cannot increase without limits his speed for two reasons:
- more the clock is fast and more it heats all things being equal, like the square of its frequency. A too great temperature can deteriorate it;
- there exists a rate where the processor becomes unstable ; its behavior becomes erratic what generally brings to plantings .
- the tendency was starting from 2004 to gather several UAL in the same processor, even several processors in the same chip. Indeed, the progressive miniaturization (see Law of Moore) allows it without much change of cost. Another tendency, since 2006 at ARM, is with the microprocessors without clock: the half of thermal dissipation is indeed due to the clock signals when the microprocessor functions; moreover, one microprocessor without clock has an almost null consumption when it does not function: the only clock signal necessary is then that intended for the cooling of the memories. This asset is important for the portable models.
- the principal functional variation today compared to the model of Von Neumann is the presence on certain architectures of two Antémémoire S different: for the instructions and for the data (whereas the model of Von Neumann specified a common memory for both). The reason of this variation is that the modification by a program of its own instructions is today regarded (except on the highly parallel machines) as a practice to proscribe. Consequently, if the contents of the mask of data must be récrit in main memory when it is modified, one knows that of the mask of instructions will have never to be it, from where simplification of the circuits and performance profit.
The instructions that the computer can include/understand are not those of the human language. The material can just carry out a limited number of well defined instructions. Typical instructions included/understood by a computer are “to copy the contents of cell 123 and to place it in cell 456”, “to add the contents of cell 321 to that of cell 654 and to place the result in cell 777” and “if the contents of cell 999 are worth 0, to carry out the instruction with cell 345”. But the majority of the instructions are composed of two zones: one indicating what to make, that one names the code operation , and the other indicating where to make it, that one names operand .
Within the computer, the instructions correspond to codes - the code for a copy being for example 001. The whole of instructions which a computer supports names its machine language , language which is a succession of binary digits , because the instructions and data which are included/understood by the CPU are only made up of 0 (zero) and 1 (one). 0 = the electric current does not pass. 1 = the electric current passes.
In general, the programmers do not use any more this type of language, but pass by what one calls a High-level language which is then transformed into binary language by a dedicated program (Interpréteur or Compilateur according to the needs). The programs thus obtained are comprehensible programs compiled by the computer in its native language.
Some computer programming languages, as the assembler are known as Low-level languages because the instructions which they use are very close to those of the computer. The programs written in these languages are thus very dependant on the platform for which they were developed. The Language C, much easier to read again than the assembler, thus makes it possible to the programmers to be more productive. For this reason, one saw it more and more used as the costs of the material decreased and that the hourly salaries of the programmers increased.
See also: Software
The computer software corresponds to broad lists of instructions given to a computer. Many programs contain million instructions, carried out for some in a repetitive way. A Personal computer of 2006 carries out several billion instructions a second.
Since the medium of the Years 1960, computers and systems conceived for this purpose made it possible to carry out several programs simultaneously. This possibility is called Multitâche. It is the case of all the computers and systems today.
Actually, the processor at the same time carries out only one program, passing from the one with the other each time necessary. If the speed of the processor is sufficiently large compared to the number of tasks to carry out, the user will have the impression of a simultaneous execution of the programs. The priorities associated with the various programs, in general, are managed by the Operating system.
See also: Operating system
The operating system is the central program which contains the basic elements necessary to the good performance of the computer.
The operating system allocates the physical resources of computer (time processor, memory, etc) to the various programs in the course of execution. It provides also tools to the other programs (like the pilots) in order to facilitate the use of different the to them peripheral without having to know the physical details of them. The principal operating systems are:
- Mac OS
Types of computers
Computer of the future.
- current Computers:
- the personal computers (PC compatible, Macintosh, Amiga, etc) :
- the desktop machines,
- the laptops,
- the shelves PC,
- Mini PC,
- PC blade ;
- personal assistants (or PDA) ;
- the average systems (midrange) (ex IBM AS/400-ISeries, RISC 6000…) ;
- the Mainframe S (central servers) (e.g.: IBM 43xx and ES9000, Siemens SR2000 and S110…) ;
- the Supercomputer s ;
- waiters in rack (1U) ;
- the work stations.
- Computer of last the.
- Machine of Turing.
- Computer exotics.
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