CPU

The CPU is the brain of a computer.Its primary function is to execute programs.Beside executing programs,the CPU also controls the operation of all other components such as memory,input and output devices.Under its control,programs and data are stored in the memory and displayed in the CRT screen or printed on the printer.

The CPU of a small computer is a microprocessor. Fig1 shows the schematic diagram of a microcomputer.The CPU of a large computer contains a number of microprocessors and other ICs on one or more circuit boards.Each microprocessor in a large CPU performs a specific task.

Fig.2 shows the schematic diagram of a CPU or microprocessor.

The major sections of a CPU are:

(i)Arithmetic and Logic Unit (ALU)

The function of an ALU is to perform arithmetic and logic operations such as addition,subtraction,multiplication,and division; AND,OR,NOT(complement) and EXCLUSIVE OR operations.It also performs increment,decrements,shift and clear operations.It also performs increment,decrements,shift and clear operations. 

(ii)Timing and control Unit 

The timing and control unit generates timing and control signals necessary for the execution of instructions. It provides status,control and timing signals necessary for the operation of other parts of the CPU,memory and I/O devices.It controls the entire operation of a computer.It is actually the control section of the CPU,which acts as the brain of a computer.

(iii)Accumulator,General and Special Purpose Registers.

cooler fan of cpu

CPU

The accumulator is a register which holds one of the operands prior to the execution of an instruction and receives result of the most arithmetic and logical operation.It is the most frequently used register.some CPUs contain a single accumulator,other contain several accumulators.General purpose registers store data and intermediate results during the execution of a program.They are accessible to programmers through instructions if they are working in an assembly language.Special purpose registers are not accessible to users.They are used by the computer for different purpose duing program execution.Examples of special purpose register are: program counter,stack pointer,ondex registers,instruction register,etc.