Central processing unit

It is well known in computer science that the words 'com­puter' and 'processor' are used interchangeably. Speaking more precisely, 'computer' refers to the central processing unit (CPU) together with an internal memory. The internal memory, con­trol and processing components make up the heart of the com­puter system. Manufactures design the CPU to control and carry out basic instructions for their particular computer.

The CPU coordinates all the activities of the various com­ponents of the computer. It determines which operations should be carried out ancl in what order. The CPU controls the opera­tion of the entire system by issueing commands to other parts of the system and by acting on responses. When required it reads information from the memory, interprets instructions, performs operations on the data according to the instructions, writes the results back into the memory and moves information between memory levels or through the input-output ports.

In digital computers the CPU can be divided into two func­tional units called the control unit (CU) and the arithmetic-log­ical unit (ALU); These two units are made up of electronic cir­cuits with millions of switches that can be in one of two states, either on or off.

The function of the CU within the centr^jpreeessor/is to transmit coordinating control signals and commands. The con­trol unit is that part of the computer that directs the sequence of step-by-step operations of the system, selects instructions and data from memory, interprets the program instructions, and controls the flow between main storage and the arithmetic-log-

The ALU, on the other hand, is that part of the computer in which the actual arithmetic operations, namely, addition, subtraction, multiplication, division and exponentiation, called for in the instructions are performed.