It is common practice in computer science for the words ‘computer‘ and ‘processor‘ to be used interchangeably. More precisely, ‘computer‘ refers to the central processing unit (CPU) together with an internal memory. The internal memory or main storage, control and processing components make up the heart of the computer system. Manufacturers 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 and in what order. The CPU can also retrieve information from memory and can store the results of manipulations back into the memory unit for later reference. 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 control unit within the central processor is to transmit coordinating control signals and commands. The control unit is that portion of the computer that directs the sequence or 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-logical unit.
The arithmetic-logical unit, on the other hand, is that portion of the computer in which the actual arithmetic operations, namely, addition, subtraction, multiplication, division and exponentiation, called for in the instructions are performed.
It also performs some kinds of logical operations such as comparing or selecting information. All the operations of the ALU are under the direction of the control unit.
Programs and the data on which the control unit and the ALU operate, must be in internal memory in order to be processed. Thus, if located on secondary memory devices such as disks or tapes, programs and data are first loaded into internal memory.
Main storage and the CPU are connected to a console, where manual control operations can be performed by an operator. The console is an important, but special purpose, piece of equipment. It is used mainly when the computer is being started up, or during maintenance-and repair. Many mini and micro systems do not have a console.
