which function does an ALU perform

ALU is the main part of CPU for perform some operations fir before knowing the functions of ALU we have to know meaning of ALU . ALU is stand for Arithmetic Logic Unit and it is perform arithmetic operation in computer. 

At its most fundamental level of computer it is consists of a control unit (CU) , an Arithmetic Logic Unit (ALU), a memory unit, and input/output (I/O) controllers So, the ALU performs simple addition, subtraction, multiplication, division, and logic operations, such as OR and AND. 

The memory stores the program’s instructions and data and the control unit fetches data and instructions from memory and uses operations of the ALU to carry out those instructions using that data.

Know how ALU work in computer - As we all know in the computer all information is stored and manipulated in the form of binary numbers, i.e. 0 and 1. Transistor switches are used to manipulate binary numbers since there are only two possible states of a switch: open or closed. An open transistor, through which there is no current, represents a 0. A closed transistor, through which there is a current, represents a 1.

The ALU has direct input and output access to the processor controller main memory and I/P devices Inputs and outputs flow along an electronic path that is called a Bus . 

The input consists of an instruction word, sometimes called a machine instruction word, that contains an operation code or "opcode," one or more operands and sometimes a format code. The operation code tells the ALU what operation to perform and the operands are used in the operation.