The part of the computer that executes program instructions is known as the processor or Central Processing Unit (CPU). The speed of a CPU chip is measured in GigaHertz (GHz) or billions of cycles per second. The speed of the computer depends on the speed of the processor. The faster the speed of the CPU chip, the faster the computer can operate. It consists of two parts - Arithmetic - Logic Unit (ALU) and Control Unit (CU).

Arithmetic Logic Unit (ALU)

ALU perform two types of operations - arithmetic and logical. Arithmetic operations include addition, subtraction,multiplication and division. Logical operations consist of comparing one data item to another to determine if the first data item is greater then, equal to or less then the other. ALU is responsible for decision making.

Control Unit (CU)

The control unit tells the rest of the computer system how to carry out a program's instruction. It directs the movement of electronic signals between memory and the ALU. It also directs these control signals between the CPU and the input/output devices. It works like a traffic policeman in the system. It controls and initiates coordination between components of the computer.