Classification of computers
1. What is a Computer?
A computer is an electronic device that accepts data (raw facts) as input, processes it under the control of a stored program, stores the result and produces information (useful output).
INPUT ──► PROCESS ──► STORE ──► OUTPUT
(keyboard) (CPU+ALU) (memory) (monitor)
Classification = grouping computers on the basis of (i) the type of data they handle, (ii) their size and processing power, (iii) their purpose and (iv) the technology/generation they belong to.
2. On the Basis of Data Handling
| Type | Works on | Result | Examples |
|---|---|---|---|
| Analog | Continuously varying physical quantities (voltage, pressure, temperature) | Approximate, no discrete values | Speedometer, thermometer, old analog computer, analog watch |
| Digital | Discrete values — only 0 and 1 | Exact and accurate; stores the program | Laptop, calculator, smartphone, digital watch |
| Hybrid | Analog input, digitally processed output | Accurate after conversion (ADC/DAC) | ECG machine, ICU patient monitor, petrol-pump dispenser, hybrid flight computer |
Analog computers measure, digital computers count.
3. On the Basis of Size and Processing Power
| Class | Size / Cost | Speed | Users | Examples | Typical use |
|---|---|---|---|---|---|
| Supercomputer | Room-size, ₹ crores | Fastest — petaFLOPS ( FLOPS) | Few, runs one giant job | PARAM Siddhi-AI, PARAM 8000, Summit, Fugaku | Weather forecasting, nuclear simulation, ISRO launch modelling, cryptography, AI training |
| Mainframe | Large cabinet | Very high, millions of simple transactions | Thousands (time-shared) | IBM z-series, IBM ES9000 | Banking core systems, railway reservation, census, insurance |
| Minicomputer / Midrange | Small cabinet | Moderate | Department level | PDP-11, IBM AS/400, VAX | Departmental server, small business (today almost merged into servers) |
| Microcomputer | Desktop / laptop / palmtop | Low to high (single microprocessor chip) | One user at a time | PC, laptop, tablet, smartphone | Personal work, education, office |
| Workstation | Desk-side | High, strong graphics | One specialist user | Sun SPARC, HP workstations | CAD/CAM, animation, scientific design |
Ordering of power: Supercomputer > Mainframe > Workstation ≈ Minicomputer > Microcomputer.
4. On the Basis of Purpose
- General purpose computer — versatile; can run any program. Example: PC, laptop, server.
- Special purpose computer — built for one dedicated job only; program is fixed in hardware. Examples: washing-machine controller, ATM, digital camera, missile guidance system, traffic-light controller.
5. On the Basis of Generation
| Gen | Period | Technology | Language | Example |
|---|---|---|---|---|
| 1st | 1940-56 | Vacuum tubes | Machine language | ENIAC, EDVAC, UNIVAC-I |
| 2nd | 1956-63 | Transistors | Assembly | IBM 1401, CDC 1604 |
| 3rd | 1964-71 | Integrated Circuits (SSI/MSI) | High level (FORTRAN, COBOL) + OS | IBM System/360 |
| 4th | 1971-present | LSI / VLSI, microprocessor | 4GL, GUI, networks | IBM PC, Apple Macintosh |
| 5th | Present & future | ULSI, AI, parallel & quantum computing | 5GL, NLP | AI chips, quantum computers |
6. Exam Points
- Differentiate analog, digital and hybrid computers with examples — 3-5 marks, very frequent.
- Classify computers by size and power; supercomputer vs mainframe vs microcomputer table — 5 marks.
- Five generations: technology + language + example in one table — 5 marks.
- Why is a digital computer more accurate than an analog computer? — 2-3 marks.
- Define general purpose vs special purpose with two examples each — 3 marks.