ALU of a computeris the place where actual execution of instructions takes place during the processing operation.
The data and instructions that are stored in primary memory are transferred as and when needed to the ALU where processing takes place.
Intermediate results generated in ALU are temporarily transferred back to primary memory.
Thus data may move between primary memory and ALU many time before processing is over.
The type and number of Arithmetic and logic operations that a computer can perform depends on engineering design of ALU.
However all ALU's are designed to perform four basic arithmetic operations add subtract multiply and divide and logic operations such as less than equal to or greater than.
Thus functions of ALU are −
It accepts data and decoded instructions from main memory and control unit.
It performs Arithmetic and logical operations on data according to instructions.
It returns the final results to main memory for storage.