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Classification of Computers

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 Anitha Padmanaban ACET

Introduction

Computers are broadly classified into

Based on Operating Principle

Based on applications

Based on size and capability

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Based on Operating Principle

Based on operating principles, computers are

divided into

 Analog Computers

Digital Computers

Hybrid Computers

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 Analog Computers

Represent data in the form of continuous

electrical signals having specific magnitude

 Allows different operation to be performed atsame time

The electronic circuit used in analog computer is

Operational Amplifier (Op-Amp)

Op-Amp is made up of  semiconductor 

integrated circuits

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Characteristic Feature of Analog

Computer 

Large voltage gain 

Voltage gain is defined as the ratio of the output voltage

to the input voltage

Infinite input resistance

Input resistance is defined as the ratio of change in input

voltage to the change in input current

Zero output resistance The output resistance is the nominal resistance

measured with no load

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IC of an Op-Amp

 Amplifier 

Input Resistor Feedback

Resistor 

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 Analog Computers

 Advantage

Very fast in their operation

 Allows several operations to be carried out at the

same time

Powerful tool that solve differential equations

Disadvantage

Does not produce accurate results

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 Analog Computer 

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Digital Computer 

 Also known as digital information processing

Stores and processes data in digital form (0’s &

1’s) 

Produce the output in digital form

Capable of processing analog data

 Analog data is converted into digital data

Conversion of digital to analog data are done by

bulit-in function

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Hardware Components

1. Arithmetic Logic Unit (ALU)

Performs various arithmetic operations like

 Addition

Multiplication

Subtraction

Division

Logic operations like AND, OR, NOT

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Hardware Components

2. Control Unit (CU)

Helps in directing the operations of ALU

3. Memory Unit (MU)

Stores data in temporary or permanent basis

4. Input Unit

Enter the data into the computer 

5. Output Unit

Displays the information generated by the computer to

the user 

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Digital Computer 

 Advantage

Faster and more reliable

Can be used in home, colleges, universities, etc

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Hybrid Computer 

Combination of analog and digital computer 

Data is measured and processed in the form of 

electrical signals and stored with digitalcomponents

Can be used to perform various types of logical

operations

 Accepts continuous input signals and convert

them into set of discrete values

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Hybrid Computer 

 Advantage

Very fast

Efficient

Reliable

Less expensive than digital computers

Disadvantage

Cost –effective to perform complex operation

 Applications Hospitals: to measure the heart beat of patient

Scientific applications, Engineering fields, Controlling business

processes

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Based on Applications

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Based on Applications General Purpose Computers

Works in all environments

Versatile

Can store number of programs

Not efficient

Consume large amount of time in generating result

Special Purpose Computers

Performs only specific function

Not versatile

Speed and memory size depend on the task to beperformed

Less expensive

Do not contain any redundant information

Efficient and consume less amount of time in

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Based on Size and Capability

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Size and Capability

Computers differ from each other in terms of shape, size and

weights

Each type of computer perform some unique functions

On the basis of size and capability, computers can be classified

into

Micro computer 

Mini computer 

Mainframe computer 

Super computer 

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Micro Computer 

Small and cheap digital computer 

Hardware Components

Built around a microprocessor, a storage unit and an

I/O channel

 Also contains power supply, connecting cables,

keyboard, mouse, printer and scanner 

Software Components

Operating system, System software and Utility

software

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Block Diagram of Micro

Computer 

Microprocessor 

Peripheral devices

Interface Circuitry

Memory

System Bus

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Microprocessor 

Heart of microcomputer 

Incorporates all the functions of CPU on to a single IC

Basic units are

 ALU

Perform various arithmetic operations

Register unit

Used to store the data and instructions temporarily needed by ALU

Includes Accumulator, Program Control, I/O, Instruction register,

Memory Address Register (MAR) and Memory Buffer Register 

(MBR)

Control unit

Used to manage and direct operations performed by

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Microprocessor 

Depending on the size the microprocessor are

further classified into

Desktop computers

Laptop computers

Hand-held computers

Etc…… 

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Memory Used to store the data and instructions

Two types of memory

Primary memory

 Also called as main memory

Used to store data temporarily

Secondary memory

 Also called as auxiliary memory

Used to store data permanently

Example

Magnetic disks, magnetic tapes, etc

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Peripheral device

They are generally the input and output devices

The various input devices are

Keyboard and mouse

The various output devices are

Monitor and printer 

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System Bus

 Also called as front side bus, memory bus, local

bus or host bus

Used to connect microprocessor, memory andperipheral device into a single unit

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Mini Computers

First introduced by Digital Equipment Corporation in

1960

Smaller in size

Can handle more data and more input and output

More powerful than micro computer 

Can support 4 to 200 users at same time

 All desktop computers can be connected to a single mini

computer 

Handle 1000s of transactions in a day

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Main frame computers

Very large computer 

Used for large scale business organizations

Capable of handling millions of records per day

Bigger and more expensive

Predecessor of servers

Occupies large space

Can maintain large databases

 Also known as super servers or database servers

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Characteristics of main frame computers

Maximum of 16 microprocessors

RAM storage lies between 128 MB and 8 GB

Run multiple operating system

Different cabinets for primary storage, secondary

storage and I/O units

Can handle huge amount of operations at the

same time

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Super Computers

Fastest type of computer 

Perform complex operations at a very high speed

Developed by Seymour Cray in 1960 at ControlData Corporation (CDC)

More expensive

Example: CRAY 3, Cyber 205, NEC SX-3 and

PARAM from India

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 Applications of Super Computers

Weather forecasting

 Animated graphics

Fluid mechanics

Nuclear energy research

Petroleum exploration