Types Of Computers

Computers are classified into various types based on purpose, technology used, size and storage capacity and historical development.  

1. Based on Purpose

According to the utilization of computer for different uses, computers are of the following two types:

a. General purpose computers 

Computers that follow instructions for general requirements, Such as sales analysis, financial accounting, invoicing, inventory, management information, etc. are called general purpose computers. Almost all computers used in offices for commercial, educational and other applications are general purpose computers.

b. Special purpose computers

Computers designed from scratch to perform special tasks like scientific applications and research, weather forecasting, space applications, medical diagnostics are called special purpose computers.

2. Based on Technology Used

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

a. 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, and to perform computations on these measurements. Analog computers are mainly used for scientific and engineering applications. Examples of analog computers are:

• Thermometer, where the mercury moves up or down as the temperature varies.

• Speedometer, where the position of the needle on dial represents the speed of the car.

b. 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 data in decimal or character form, it is converted into binary digits (0s and Is). Almost all the computers used presently are digital computers.

c. Hybrid computers

Hybrid computers incorporate the technology of both analog and digital computers. These computers store and process analog signals that are 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 (for example, process control).

3. Based on Size and Storage Capacity
According to the size and memory/storage capacity, computers are of the following four types:

a. Supercomputer

Supercomputer is the biggest and fastest computer, which is mainly designed for complex scientific applications. It has many CPUs (central processing units-main parts of a computer) which operate parallel, making it the fastest computer. It is the most expensive and sophisticated computer that executes complex calculations at the fastest speed. It can process huge amounts of scientific data.

Applications of supercomputer

A supercomputer is used for various applications in areas of weather information, petroleum exploration and production, energy management, defense, nuclear energy research, structural analysis, electronic design, real-time animation and medicine.

Features of supercomputer

A supercomputer has the following capabilities:

• It contains many CPUs operating parallel with processing speed in the range of 400-10,000 MIPS (millions of instructions per second).

• It maximises the number of floating point instruction per second (FLOPS) which is usually above 1 gigaflop per second.

• It has a very high memory and hard disk capacity. Entire memory of a supercomputer consists of high speed.

• Its cycle time is as low as 4 nano second (ns). Thus, it can add two 64-bit data in a single machine cycle.

Examples

• Param 8000, 9000 and 10000 (Figure 1.7), developed by C-DAC, India.

• CRAY X-MP/14,24, 48 and CRAY Y-MP8D (Figure 1.8), developed by Control Data Corporation

• SX-2 & SX-3R, developed by Nippon Electric Corporation

• HITAC S-300, developed by Hitachi, Japan

• VPP 300, developed by Fujitsu

b. Mainframe computer

Mainframe computers are very large and fast computers but smaller and slower than supercomputers. They are used in a centralised location where many terminals (input/output devices) are connected with one CPU, and thus, allow different users to share the single CPU. They have a very high memory (several hundred megabytes) and can support thousands of users.

Applications of mainframe computers

They are mainly used for applications like railway and airline reservations, banking applications and commercial applications of large industries/companies

Features of mainframe computer

A mainframe computer has the following capabilities:

• It has very large disks that can store several gigabytes of data.

• It has a very high memory for storing several hundred megabytes.

• It needs a controlled climate. Therefore, a mainframe computer is stored in special secure room.

• It can have thousands of terminals (monitor and keyboard).

• It costs several million rupees.

Some examples of mainframe computers are

• IBM 3090, 14381 and 14300

• IBM ES 2000 and 9000

• DEC 10,000

Minicomputers

They are of medium scale, smaller and generally slower than mainframe computers. Like mainframes, they have many terminals, which are connected with one CPU and can support many users. The cost of a minicomputer is less as compared to mainframe. Therefore, it is mainly used in applications where processing can be distributed among several minicomputers rather than using a mainframe computer.

Features of minicomputer

A minicomputer provides the following features:

• It has smaller disks and lesser memory than a mainframe computer.

• Its processing speed is generally slower than a mainframe computer.

• Like mainframes, it can support thousands of users with separate terminals.

• It costs several lakh rupees.

Examples

Some examples of minicomputers are

• PDP-1

• DEC Micro VAX

• IBM AS/400 (actually a midicomputer-a computer with performance between a mainframe and minicomputer)

c. Microcomputers

A microcomputer is the smallest digital computer, which uses a microprocessor as its CPU. Microprocessor is a single chip (integrated circuit) CPU. Microcomputer is popularly called as personal computer (PC). It can be used both as a stand-alone machine and a terminal in a multi-user environment. Microcomputers are becoming very popular nowadays due to very high processing power and memory.

Microcomputers are either of desktop or portable models. Portable computers can be carried from one place to another. Some of the models are called laptops while others notebook computers. Notebook computers (popularly called as tablets) are smaller, lighter and costlier than laptops. Personal digital assistants (PDAs), popularly called digital diaries, are also notebook computers with built-in software for appointments, electronic mail and scheduling. Desktop computers fit on a desktop and are used widely in offices and homes. The pictures of some of the desktop and portable computers are shown in Figure 1.9.

There are many types and models of personal computers, which are described in table 1.2

4. Based on History

a. First Generation Computers

In the period of the year 1940-1956, it was referred to as the period of the first generation of computers. These machines are slow, huge, and expensive. In this generation of computers, vacuum tubes were used as the basic components of CPU and memory. Also, they were mainly dependent on the batch operating systems and punch cards. Magnetic tape and paper tape were used as output and input devices. For example ENIAC, UNIVAC, EDVAC etc.

b. Second Generation Computers

The were period of the year, 1957-1963 was referred to as the period of the second generation of computers. It was the time of the transistor computers. In the second generation of computers, transistors (which were cheap in cost) are used. Transistors are also compact and consume less power. Transistor computers are faster than first-generation computers. For primary memory, magnetic cores were used, and for secondary memory magnetic disc and tapes for storage purposes. In second-generation computers, COBOL and FORTRAN are used as Assembly language and programming languages, and Batch processing and multiprogramming operating systems are allowed in these computers.

For example IBM 1620, IBM 7094, CDC 1604, CDC 3600, etc.

c. Third Generation Computers

In the third generation of computers, integrated circuits (ICs) were used instead of transistors(in the second generation). A single IC consists of many transistors which increased the power of a computer and also reduced the cost. The third generation computers are more reliable, efficient, and smaller in size. It used remote processing, time-sharing, and multiprogramming as operating systems. FORTRON-II TO IV, COBOL, and PASCAL PL/1 were used which are high-level programming languages.

For example IBM-360 series, Honeywell-6000 series, IBM-370/168, etc.

d. Fourth Generation Computers

The period of 1971-1980 was mainly the time of fourth generation computers. It used VLSI(Very Large Scale Integrated) circuits. VLSI is a chip containing millions of transistors and other circuit elements and because of these chips, the computers of this generation are more compact, powerful, fast, and affordable(low in cost). Real-time, time-sharing and distributed operating system are used by these computers. C and C++ are used as the programming languages in this generation of computers.

For example STAR 1000, PDP 11, CRAY-1, CRAY-X-MP, etc.

e. Fifth Generation Computers

From 1980 - to till date these computers have been Internet used. The ULSI (Ultra Large Scale Integration) technology is used in fifth-generation computers instead of the VLSI technology of fourth-generation computers. Microprocessor chips with ten million electronic components are used in these computers. Parallel processing hardware and AI (Artificial Intelligence) software are also used in fifth-generation computers. The programming languages like C, C++, Java, .Net, etc. are used.

For example Desktop, Laptop, NoteBook, UltraBook, etc.

Computers of the future

Information technology is changing very fast. Can you imagine computers of the future? The future computer would have artificial intelligence, would be mobile and as small as atoms or molecules. We have already discussed the fifth generation computers having artificial intelligence. Let us discuss about mobile and nanotech computers in brief.

a. Mobile Computers

In future, mobile computing will become ubiquitous. A specification for a handheld device markup language (HDML) for mobile computers with screens similar to those in cellular telephones has been proposed to W3 Consortium, the organisation that develops new versions of the hypertext markup language (HTML). HDML will make cellular phones smarter, allowing people to use wireless communications

The currently available mobile global positioning system (GPS) devices enable people to use satellite data to determine their location within a few yards anywhere on earth. Mobile computers with GPS capability will be a boon to anyone who is lost or in unfamiliar territory, travellers, sailors, lost children, police, and troops behind enemy lines.

b. Nanotech Computers

Researchers in laboratories around the world are working towards the construction of nanotech computers, consisting of individual atoms or molecules. The science of such atomic-level construction is known as nanotechnology. Scientists expect to be able to build microscopic computers that would be more powerful than the desktop computers of today and supercomputers that can be worn like a wristwatch. The possible application of nanotech computer is something that is presently beyond our imagination. For instance, such computer can be programmed in such a manner that they could be injected into the human blood to destroy viruses.