Computers can be classified into three categories based on their functions: analog computers, digital computers, and hybrid computers. Analog computers operate on continuously varying physical quantities while digital computers operate using discrete signals represented by numbers. Hybrid computers combine aspects of analog and digital computers by using a modem to convert between signal types. Computers can also be classified based on size into four groups: super computers, mainframe computers, mini computers, and micro computers with each category increasing in portability and decreasing in processing power and number of simultaneous users.

2. On the basis of functions: Computers can be classified into three different
categories :
1. ANALOG COMPUTERS
2. DIGITAL COMPUTERS
3. HYBRID COMPUTERS

3. ANALOG COMPUTERS :
It operates on mathematical variables that change
with continuously varying physical qualities such as,
electric current, pressure, temperature, time etc.
Such computers are single-problem-oriented that is
specific to a particular task.

4. DIGITAL COMPUTERS :
It operates with the discrete (discontinuously
varying) signals in the form of numbers
especially zeros and ones. Such computers
are many problems oriented Ex: IBM-PC,
Apple, Macintosh, and other available in the
market.

5. HYBRID COMPUTERS :
It is a combination of analog and digital computers.
Which uses a special device called MODEM to
convert analog signal to digital and vice versa. The
full form of MODEM is Modulator and Demodulator.
Information can be transferred to geographically
dispersed areas through computers by the use of
MODEM.

7. On the basis of size: Computers are classified into
Four groups according to their size and speed.
1.Super Computers
2.Mainframe Computers
3.Mini Computers
4.Micro Computers

8. Super Computers :
They are the fastest and the most expensive
machines, and are considered national
resources. Some of the areas in which super
computers are being used are Weather
forecasting, biomedical research and aircraft
design.

9. Mainframe Computers
Mainframes are installed in large rooms. It occupies a
large amount of space due to its accompanying services
such as banks of magnetic disk, magnetic tape, high-
speed printers, modems and several terminals. It can
perform very complex scientific calculations, and they
are mostly used for scientific purposes. They are also
used where the company has its operations in different
cities or different countries, such as Banks, such as
Credit Card companies. More than 100 users can work
at a time simultaneously without degrading its
performance.
Ex: CYBER-76,IBM 3000, UNIVAC 1180 etc

10. Mini Computers
Physically it may be smaller, in comparison, to
the Mainframe, Like the Mainframe; many users
can simultaneously work on them. It is used for
controlling manufacturing processes. They are
mainly used in large business houses.
Ex POP 11/73, HP 300,VAX 11,PRIME etc.

11. Micro Computer :
We can accommodate it on a desk and only one
person can use it at time. Therefore, the term
Personal Computer (PC) has been given to such
computers. These are used for small business,
office administration purpose and even in playing
games.
EX: IBM PC XT/AT, COMPAQ,ACER AST EPSON etc