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Program control principle. The program consists of command set which is fulfilled by the processor automatically one after another in certain sequence.

Sampling of the program of storage is carried out by means of the instruction counter. This register of the processor sequentially increases the storable address in it by the length of a command. And as program commands are allocated in the storage one after another, the sampling of a chain of commands of sequentially allocated storage cells thereby will be organized. If it is necessary to pass after command performance not to the following command, but to any other one, commands of the conditional or unconditional passages which bring number of the storage cell containing the following command in the instruction counter are used. Sampling of commands of storage stops after achievement and performance of a command «feet». Thus, the processor executes the program automatically, without interference of the person.

General device of computers

Let's provide the computer device diagram.

 

 

Fig 4.1 – Architecture of a computer by Von Neumann's principle

 

The control and arithmetic-logic device in modern computers are united in one block – the processor which is the converter of the information, arriving of memory and external devices (sample of commands of memory, coding and decoding, performance of various operations, and the coordination of work of knots of the computers).

Memory (AM) stores the information and programs. A memory at modern computers is multifunctional: RAM stores that information from which computers works directly at present, ESD has much bigger capacity than RAM, but with essential slower access, SRAM (scratch-pad) and ROM.

The command is an activity description which the computer shall execute. As a rule, the command has a code (reference designation), basic data (operands) and result.

The variety of modern computers is very great. But their structures are based on the general logical principles allowing the selection in any computer of the following principal devices:

• memory (the storage device, the memory) consisting of the renumbered cells;

• the processor including a control unit (CD)

• arithmetic and logic unit (ALU);

• input equipment;

• output device.

These devices are connected by communication links on which information is transferred. The main devices of the computer and communication are given in the diagram. Bold arrows show the ways and directions of movement of information, simple arrows – the ways and directions of transmission of controlling signals.

Memory functions:

a) information reception from other devices;

b) information storage;

c) output of information on request in other devices of the machine.

 

 
 

 


Processor functions:

a) data handling according to the given program by execution of arithmetical and logical actions;


Date: 2015-12-24; view: 238


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