Posts Tagged ‘Processor Unit’

The central processing unit

Friday, August 13th, 2010

Instructions stored in main computer storage control the operations which occur within the central processing unit. The central processing unit (CPU) is the heart of the computer system. It contains the electronic circuitry which actually causes processing to occur. The CPU interprets the instructions in a computer program, performs the calculations and the moving of data as specified by the program, and controls the input/output operations of the system.

The central processing unit, of course, is a part of the processor unit. The CPU consists of two major components: the arithmetic/logic unit and the control unit.

The arithmetic/logic unit contains the electronic circuitry necessary to perform arithmetic operations such as addition, subtraction, multiplication, and division. It also contains the circuitry required to perform logical operations such as comparing one number to another and indicating the results of that comparison.

The control unit directs and coordinates the entire computer system. Its tasks Include controlling the Input/output units, controlling the opera tions of the arithmetic/logic unit in the CPU, and transferring data to and from main computer storage.

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Computer instructions

Wednesday, August 11th, 2010

The operations performed by a computer are controlled by a computer program. A computer program consists of instructions to the electronics of the computer system to process data in some manner. Program instructions are stored in main computer storage as machine language instructions which the electronic circuits of the computer system can interpret and execute. A Knowledge of the basic characteristics of machine language instructions is useful in understanding how a computer operates.

A machine language instruction is composed of: 1) An operation code; 2) Values indicating the number of characters to be processed by the instruction; 3) The addresses of the data to be used in the processing.

The operation code is a unique value which is typically stored in a single byte. This unique value indicates to the computer electronics what operation is to occur. For example, the letter of the alphabet “A” stored as the operation code might indicate that an addition operation is to occur. The letter “0” might mean that division is to take place.

The number of characters to be processed must be included in a computer instruction so that the electronic circuitry of the processor unit will reference the proper number of digits in the field to be processed. For example, if a four digit field were to be added to another four digit field, the number of characters specified in the instruction for each field would be four.

The locations of the fields involved in the operation must be specified in the instruction. This enables the circuitry to identify where in storage the data to be processed is located.

Although the formats of computer instructions vary a great deal between different computer systems, the basic elements of operation code, number of characters to process, and the addresses of the data to be processed will almost always be present.

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