1.1.4 CLASSIFICATION OF COMPUTERS

Computers are classified into various types based on historical development (computer generation), purpose, technology used, and size & storage capacity. The following figure illustrates the classification of computers based on different criteria.

 

Classification of computer based on

 

Fig 04: classification of computer based on different criteria

 

Historical Development (Computer Generations):

First Generation Computers (1940-1956) Vacuum Tubes

·         The first business computer was developed in the year 1951 by U.S. Census Bureau. This computer was called Universal Automatic Computer (UNIVAC).

·         The computers that used vacuum tube circuits were called the First Generation computers.

·         The vacuum tube circuits contained a filament that was heated to emit electrons.

Outstanding features:

1.      Very expensive

2.      Bulky in size and occupied a lot of space

3.      Magnetic core memories

4.      Main application areas were scientific computation, record keeping, pay roll processing etc.

5.      Processor speed measured in milliseconds.

Second Generation Computers (1956-1963) Transistors

·         Bell labs of USA invented transistors that were used in place of vacuum tubes.

·         Transistors are electronic circuits that are small in size and do not require any heating for emitting electrons.

Outstanding features:

1.      Smaller in size in comparison with the previous generation and generated less heat.

2.      Internal storage capacity was increased and processor speed measured in microseconds.

3.      Magnetic core memories as primary storage.

4.      Machines started to evolve as series rather than standalone processors.

5.      More reliable and less prone to errors.

Third generation computers (1964-1971) Integrated Circuits

·         These used Large Scale Integrated (LSI) circuits for processing.

·         LSI circuits integrate several circuits’ components into a single chip.

Outstanding features:

1.      Smaller in size

2.      Significant improvement in cost performance factor.

3.      Could be commercially produced at cheaper rates.

4.      Processor speeds measured in nano seconds.

5.      Portable.

6.      The use of high level languages e.g. COBOL, FORTRAN and PL/1.

7.      Disk used as backing store medium.

8.      Complex and sophisticated technology used for CPU design.

Fourth Generation Computers (1971-Present) Microprocessors

·         Very Large Integrated (VLSI) chips were invented in the year 1969.

·         The introduction of standard architecture helped in greater mobility of systems.

Outstanding features:

1.      Very small in size and very reliable and cheaper.

2.      Development of microprocessor based technology.

3.      Semiconductor memory used.

4.      Sophisticated systems software.

5.      Personal and home computers availability.

6.      Complex and sophisticated technology used for CPU design.
 

Fifth Generation Computers (Present and Beyond) Artificial Intelligence

·         Recent research has focused on developing ‘thinking computers’ i.e. artificial intelligence.

·      These will have VVLSI (Very Very Large Integration) technology with sophisticated operating system interface capability. These computers will have KIPS (Knowledge Information Processing System).

In reality we have entered the era of generation less computers because no single innovation is, or will be, good enough to name another generation of computers.

 

Classification By Purpose:

There are some needs that are specified to a particular environment or a particular user whereas, there are many needs that are desired by every user of the computer. Depending upon the purpose of use, the computers can be general purpose or special purpose.

General Purpose Computers

·         General purpose computers are the computers that can be used for all general needs of all environments and users.

·         These are the versatile computers that can perform a variety of jobs for all types of environments. 

·         The programs or instructions are fed to them and at the time of execution these computers process these instructions and produce meaningful results.

·         For example, a personal computer that is capable of calculating accounts data, preparing students result, designing broachers, writing letters, accessing Internet or playing games is a general purpose computer.

Special purpose computers:

·         Special purpose computers are the computers that are specially designed to perform a specific environment.

·         These are designed for performing a particular task and cannot perform other tasks.

·         These computers are not versatile.

·         The instructions used by these computers are generally embedded in various automatic devices.

·         For example, a computer designed to display the path and trajectory of a missile can be only used for this purpose and we cannot use it for playing games. A computer that has been designed to count the telephone call pulses and the amount to be paid can only serve this purpose. We cannot use it for designing and word processing.

 

Classification By Technology Used

According to the technology used, computers are of following three types:

1.      Digital computers

2.      Analog computers

3.      Hybrid computers

Digital Computers:

·         Digital computers are mainly general purpose computers that represent and store data in discrete quantities or numbers.

·         In these computers, all processing is done in terms of numeric representation (binary digits) of data and information.

Although the user enters the data in decimal or character form, it is converted into binary digits (0s and 1s).

·         For example: PC, Laptop etc.

PCs (Microcomputers) are of several types: desktop PCs, tower PCs, laptops ( or notebooks) and personal digital assistants- handheld computers or palmtops.

Desktop PCs are those in which the case or main housing sits on a desk, with keyboard in front and screen (monitor) often on top.

Tower PCs are those in which the case sits as a “tower”, often on the floor beside a desk, thus freeing up desk surface space.

Notebook computers, also called laptop computers, are light weight portable computers with built-in-monitor, keyboard, hard disk drive, battery, and AC adapter that can be plugged into an electrical outlet. They weigh anywhere from 720 gms to 3.6 Kgs.

Personal digital assistants (PDAs), also called handheld computers or palmtops, combine personal organization tools- schedule planers, address books, to-do lists- with the ability in some cases to send e-mail and faxes. Some PDAs have touch sensitive screens. Some also connect to desktop computers for sending or receiving information.

Analog Computers:

·         Analog computers are special purpose computers that represent and store data in continuously varying physical quantities such as current, voltage or frequency.

·         These computers are programmed for measuring physical quantities like pressure, temperature, speed, etc., and to perform computations on these measurements.

·         Analog computers are mainly used for scientific and engineering applications.
 

Some of the examples of Analog computers are given below:

Thermometer: It is a simple analog computer used to measure temperature. In thermometer, the mercury moves up or down as the temperature varies.

Speedometer: Car’s speedometer is another example of analog computer where the position of the needle on dial represents the speed of the car.

Limitations of the Analog computer:

1. These do not have logical facilities afforded by programming.
2. They do not have the ability to store data in large quantities.
3. Cost of implementation of computation ios very high.

Hybrid computers:

·         Hybrid computers incorporate the technology of both analog and digital computers.

·         These computers store and process analog signals which have been converted into discrete numbers using analog to digital converters.

They can also convert the digital numbers into analog signals or physical properties using digital to analog converters.

·         Hybrid computers are mainly used in artificial intelligence (robotics) and computer aided manufacturing (e.g., process control).

·         For example, money counting machine and Automated Teller Machine (ATM).

 

Classification by Size and Capacity:

Computers are classified into different types depending on the memory size, cost and processing speed.

Fig 05: Classification of computers on the basis of memory size, cost and processing capabilities

 

The performance of a computer involves speed of processing data, storage capacity and ability to handle input and output devices.

Microcomputers:

• Microcomputers are also called personal computers (PCs) and use microprocessor as its CPU, a memory unit, and input device and an output device.
• They are small in size. Also, they do not have large storage capacities. The word length of a microcomputer lies in the range 8-32.
• They can perform difficult task. They are used for general purpose calculations, industrial control, home appliances, desktop publishing, graphics designing and project management.
• These are of two types- Desktops and Portables.
• Few examples are IBM PC, PS/2, Apple II and Macintosh.

Minicomputers:

• Minicomputers are faster and more powerful than microcomputers. Their word length is 32 bits (word length means number of bits in a computer word).
• These computers can perform more complex tasks and cost more than microcomputers.
• They are larger in size and their storage capacity is small to medium.
• They are used for payroll preparation, accounting and scientific computation, controlling and monitoring production processes.
• Few examples are VAX 11, PDP11/42 and WIPRO LANDMARK 860 etc.

Mainframes:

• These are more powerful than minicomputers. Their word length may be 48, 60 or 64 bits.
• They have high processing speeds and can store large amounts of data.
• They are used in research organizations, large industries, large business and government organizations, banks and airline reservations where large database is needed. However, these computers consume more electricity.
• Few examples are IBM 2000 series and UNIVAC 1180.

Super Computers:

• These are the largest and fastest computers. Their word length is 64-96 bit. They are also the costliest.
• A super computer has a number of CPUs which operate in parallel to make it faster.
• They are used for massive data processing and solving very sophisticated problems i.e., in the fields of science and defense, designing and launching missiles, weather forecasting, biomedical research, aircraft design and automobile design.
• Few examples are CRAZY 3, HITAC S-300 etc. India has a series of super computers called PARAM developed by C-DAC and ANURAG. Wipro InfoTech has developed Supernova computers.