Microprocessor Introduction

What is a Microprocessor

The word microprocessor was introduced by Intel Corporation. 4004 was the first commercial microprocessor by Intel on November 1971. A microprocessor is a single chip CPU which contains control and logic circuits. It is capable of performing arithmetic and logical operations. It consists of an arithmetic and logical unit, register unit and control unit. These three units are fabricated on single chip. These are generally categorized by speed, word length, architecture and instruction set.

All the microcomputers (PCs) are developed around the microprocessors. So, it is supposed to be the heart of any computer. Whether it is a desktop machine, a server or a laptop.


The functional block diagram of a microcomputer is shown in figure. It consists microprocessor, Input or Output interface, RAM and ROM memory, bus decoder and bus system.

Microprocessor system block  diagram
Microprocessor system block diagram


It is the CPU of a microcomputer system. It consists of an ALU, a register unit and a control unit. This is responsible for carrying out arithmetic and logical operations as for providing the control signals for system operation.

l/O Interface

The IO interface is the media through which the microprocessor communicates with the outside world. The ports are normally programmable and are part of the I/O interface chip.


To store a program and data, microprocessor requires a memory unit. The memory section of a microcomputer system consists of two types of memories. These are read/write or random-access memory (RAM) and read only memory (ROM). RAM is read/write semiconductor memory. In random access memory the time taken to access any memory location is the same. This memory is volatile and holds the program and data in current use.


Read only memory (ROM) is non-volatile. This type of memory contains firmware, such as the executive program. It runs when a system is switch on and data which need not be alter.

Bus System

To communicate with the I/O and the memory devices (these devices are peripheral devices) processor requires some connections between the processor and the peripheral devices. The connections or wires or lines are viz. the bus system. These bus system carries three types of information, i.e., address, data and control and, hence, it consists of three types of buses. These are address bus, data bus and the control bus.

Address bus

For an 8-bit microprocessor the address bus is about 16-bits. The address bus is unidirectional and emanates from the microprocessor. Its purpose is to select memory locations in RAM or ROM and I/O ports

Data bus

The data bus is bidirectional and its size depends on the microprocessor word size. The data bus carries information to and from the microprocessor, for example, to/from memory or to/ from input/output ports.

Control bus

The control bus provides signals to control the operation of the system. This bus is rather complex, being about 10-bits wide and some signals are bidirectional. The clock and R/W signals are part of the control bus.

Address decoder

This circuit uses the most significant bits of the address bus to select devices (ROM, RAM I/O chips). Then the address bus lower bits select the appropriate location(s).

We will discuss the microprocessor in detail in upcoming articles. So stay tuned with us we will back with another article soon.