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Generally, the words ‘microprocessor’ and ‘microcomputer’ are used to correspond to the same thing, but in fact these words have different meanings. The microprocessor is an integrated circuit (IC) developed based on LSI or VLSI technology. It is the core of any computer system, but the microprocessor by itself is completely useless, until external peripheral devices are connected with it to interact with the outside world. The microcomputer is a complete computing system and it is built with a microprocessor, input/output devices and memory (RAM and ROM).


Arithmetic/Logic Unit (ALU)

The ALU performs arithmetic operations such as addition, subtraction, multiplication, and division and logic operations, namely, AND, OR, XOR, complement, rotate and shift. After the operations, results must be stored either in a specified register or in the memory.



The microprocessor has various general-purpose registers such as B, C, D, E, H, L, and the Accumulator (A). These registers are used to store data and addresses temporarily during the execution of a program.


Timing and Control Unit

The timing and control unit provides the necessary timing and control signals to perform any operation in the microcomputer. Actually, it controls the flow of data between the microprocessor and memory/peripheral devices.


Input Devices

The input devices transfer data in binary form the outside world to the microprocessor. The most commonly used input devices are keyboard, switches, mouse, scanner, and analog-to-digital converter.

Schematic block diagram of a microcomputer



Architecture of a microcomputer



The output devices transfer data from the microprocessor to any output device such as a printer, plotter, monitor, or magnetic tape.



The memory unit stores the binary information such as instructions and data, and provides that information to the microprocessor for processing. To execute any instruction, the microprocessor reads instructions and data from memory. After the computational operations in the ALU, microprocessor again stores results in the memory for further use.


System Bus:Address Bus, Data Bus and Control Bus 

The microprocessor always communicates with input/output devices and the memory with some path called the system bus. The system bus consists of the Address Bus, Data Bus and Control Bus. The address bus is used to locate any input/output devices and memory. The Data bus is used to transfer data in binary form between the microprocessor and peripherals. The microprocessor communicates with only one peripheral at a time. The timing signals are provided by the control bus of the microprocessor.


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