Explain functional units of computer system in detail.

Input unit

The input unit takes data and instructions from the user and converts them into binary form that the computer can use. Keyboard, mouse, scanner and microphone are examples. The data is placed in memory or sent to a register of the CPU. Input is usually read one character or one word at a time.

Memory unit

The memory stores programs and data. It has two levels. The main (primary) memory, made of semiconductor RAM, is fast and holds the programs now being run. It is directly used by the CPU. The secondary memory, such as a hard disk or SSD, is larger and cheaper but slower. It keeps programs and data permanently. Each word of main memory has an address, and the CPU can reach any word by giving its address.

Arithmetic and logic unit (ALU)

The ALU does the arithmetic operations such as add, subtract, multiply and divide. It also does logic operations such as AND, OR, NOT and comparison. The operands come from registers. The result goes back to a register. A set of flag bits records things like zero, carry and overflow.

Control unit

The control unit is the brain of the computer. It reads each instruction from memory, decodes it, and sends the right timing and control signals to the other units. It tells memory when to read or write, tells the ALU what to do, and tells the input and output devices when to transfer data. It does not process data itself. The program counter (PC) holds the address of the next instruction, and the instruction register (IR) holds the present one.

Output unit

The output unit shows the results to the user in a form that people can understand. Monitor, printer and speakers are examples. It receives the binary results from the memory or CPU and converts them.

Interconnection

The units are joined by the system bus, which has an address bus, a data bus and a control bus. Data goes from the input unit to memory, then through the ALU, then back to memory and out through the output unit. The control unit directs the whole flow.

Working in short

A program is first loaded into memory through the input unit. The control unit fetches an instruction, decodes it and fetches the operands. The ALU does the work and the result is stored or displayed. This fetch, decode and execute cycle repeats until the program ends.