Introduction to MicroProcessor | Block Diagram Features and Working Process

Microprocessors have been one of the most used methods of incorporating intelligence into automated devices. Their general-purpose nature, speed, and size have made them one of the most common components in Computer Science Engineering. It is, therefore, necessary to develop a good understanding of their operation and how they can be used as building blocks for automated systems and control applications. A microprocessor is a controlling unit of a micro-computer, fabricated on a small chip capable of performing ALU(Arithmetic Logical Unit) operations and communicating with other devices connected to it.

Introduction to MicroProcessor

The microprocessor consists of an ALU, register array, and a control unit. ALU performs arithmetical and logical operations on the data received from the memory or an input device. Register array consists of registers identified by letters like B, C, D, E, H, L, and accumulator. The control unit controls the flow of data and instructions within the computer.

The microprocessor is a programmable integrated device that has computing and decision-making capability. the work programmable specifies that the microprocessor can be instructed to perform different operations according to a given program. 'Integrated' means a microprocessor is a combined unit of different blocks that perform various operations. The basic block diagram of a microprocessor is shown below with its three internal segments - ALU, Register Array (RA), and Control Unit (CU).

Block Diagram of a Basic Microcomputer


Arithmetic Logi Unit (ALU)

This block of the microprocessor is responsible to perform arithmetic operations addition, subtraction, etc., and logical operations (AND, OR, EX-OR, Complement, etc). ALU is the unit that decides the capability of any microprocessor.

Register Array (RA)

The microprocessor consists of various registers. the collection of registers is named register array. these registers are primarily used to store data temporarily during the execution of a program. same registers are used to hold the input and output data and are accessible to the user through the instructions.

Control Unit (CU)

The control and timing signals are generated by the control unit. it controls the flow of data between the microprocessor and others like memory and peripherals.

The microprocessor takes the instruction and data from the memory and input unit respectively. after processing, the result is given to the output unit. the main processing job is done by the microprocessor but this, it requires the association of memory and I/O units. there are three basic components that comprise a microprocessor system to perform a given task.

  1. Microprocessor
  2. Memory
  3. Input/Output devices

Introduction to MicroProcessor | Block Diagram Features and Working Process

Working of Microprocessor

The microprocessor follows a sequence: Fetch, Decode and Execute.

Initially,  the instructions are stored in the memory in sequential order. Th microprocessor fetches those instructions from the memory, then decodes them, and executes those instructions till STOP instruction is reached. Later, it sends the result in binary to the output port. Between these processes, the register stores the temporary data, and ALU performs the computing functions.

List of Terms used in a Microprocessor:

Here is a list of some of the frequently used terms in a microprocessor-

  • Instruction Set - It is the set of instructions that the microprocessor can understand.
  • Bandwidth - It is the number of bits processed in a single instruction.
  • Clock Speed - It determines the number of operations per second the processor can perform. It is expressed in megahertz(MHz) or gigahertz(GHz). It is also known as Clock Rate.
  • Word Length - It depends upon the width of the internal data bus, registers, ALU, etc. An 8 - bit microprocessor can process 8-bit data at a time. The word length ranges from 4 bits to 64 bits depending upon the type of the microcomputer.
  • Data Types - The microprocessor has multiple data types formats like binary, BCD, ASCII, signed, and unsigned numbers.

Features of Microprocessor:

Here is a list of some of the most prominent features of any microprocessor - 

  • Cost-effective - The microprocessor chips are available at low prices and resulting in their low cost.
  • Size - The microprocessor is of small size chip, hence is portable.
  • Low Power Consumption - Microprocessors are manufactured by using metal oxide semiconductor technology, which has low power consumption.
  • Versatility - The microprocessors are versatile as we can use the same chip in a number of applications by configuring the software program.
  • Reliability - The failure rate of an IC in microprocessors is very low, hence it is reliable.

A microprocessor can be classified into 3 categories ( types of the microprocessor ) - 


RISC Processor

RISC stands for Reduced Instruction Set Computer. It is designed to reduce the execution time by simplifying the instruction set of the computer.

CISC Processor

CISC stands for Complex Instruction Set Computer. It is designed to minimize the number of instructions per program, ignoring the number of cycles per instruction.

Special Processors

These are the processors which are designed for some special purposes. For example - Coprocessor, I/O Processor, Transputer(Transister Computer), Digital Signal Processor.

Development in microprocessor

The advent of microprocessors was accidental. Intel corporation founded by Moore and Noyce in 1968 was initially focused on creating semiconductor memory. Ted Hoff, an intel engineer felt that a general-purpose logic device could replace the separate multiple components. this idea led to the development of the first microprocessor.

Federico Faggin and Stanley Mazor realized this idea into hardware at Intel. the result was the intel 4000 family comprising the 4001 (2K ROM), the 4002 (320 bit RAM), the 4003 (10-bit I/O shift register), and the 4004, a 4-bit central processing unit (CPU). Intel introduced the 4004 microprocessor to the world in November 1971. It was not truly a general-purpose microprocessor as it was basically designed for a calculator.

The continuous development in integration technology made it possible to accommodate more and more gates in a single chip. as a result, it is possible for a small microprocessor chip to perform more number of operations with a high degree of complexity. the intel after its first microprocessor, subsequently came out with 8008, 8080, 8085, 8086/88, 80186/188, 80286, 80386, 80486, and Pentium series of microprocessors, each with more capabilities than its predecessor. The below table gives the intel's journey of microprocessors from 4004 to Pentiums.

Intel Microprocessor

MicroprocessorYearWord sizeMemory CapacityClock Speed
400419714-bit1 KB750 kHz
800819728-bit16 KB800 kHz
808019738-bit64 KB2 MHz
808519768-bit64 KB3-6 MHz
8086197816-bit1 MB5-10 MHz
808819808/16-bit1 MB5-8 Mhz
8018619828/16-bit1 MB6-8 MHz
8018819828/16-bit1 MB6-8 MHz
80286198216-bit16 MB real 4 GB virtual6-12.5 MHz
80386 DX198532-bit4 GB real 64 TB virtual20-33 MHz
80386 SX198816/32-bit16 MB real 64 TB virtual20 MHz
80486198932-bit4 GB20-100 MHz
Pentium199364-bit4 GB60-133 MHz
Pentium Pro199564-bit64 GB150-200 MHz
Pentium-MMX199764-bit64 GB166-233 MHz
P-II199764-bit64 GB233-450 MHz
P-III199764-bit-650 MHz-1.2GHz
P-IV2000/2001--1.3-2.0 GHz

Motorola is another manufacturer of microprocessors. the Motorola has its very popular 68 series microprocessor. below given shows the various microprocessor by Motorola.

Motorola Microprocessor

MicroprocessorYearWord sizeMemory CapacityClock Speed
680019748-bit64 KB1 MHz
680919798-bit64 KB4-8 MHz
68000197916/32-bit(232 new version)10-25 MHz
68010198332-bit16 MB
68020198432-bit4 GB12.5-33 MHz
98030198732-bit4 GB20-33 Mhz
98040-64-bit4 GB20-25 MHz
98060-64-bit4 GB + 16K Cache-
Power PC-64-bit4 GB + 32K Cache-

Other better-known microprocessors are Toshiba's T3472 (4 bit), NEC's mueCOM4 (4 bit), Zilog Corporatio's z80 (8 bit), Fairchild's F8 (8 bit), Texas instrument's TMS 9940 (16 bit) and Zilog's Z8000 (16 bit).

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