What is a Computer ?
A computer is an electronic device that manipulates information, or data. It has the ability
to store, retrieve, and process data. You can use a computer to type documents, send email, and
browse the Web. You can also use it to handle spreadsheets, accounting, database management,
presentations, games, and more.

Broad Categories of computer
Computer is divided into three broad categories, and a category has its own categories as given
below :
On the basis of Work: Digital, Analog and Hybrid Computer:
S1Digital Computer
N Computer that uses binary
     digits to display discreet
     information is called
     digital computer.
Information is in discreteform. It displays information in the form of text, graphics, and pictures.
Analog Computer
Computer that uses analog signal to display information
   is called Analog computer.
Hybrid Computer
        A computer that is able to understand Binary and Analog signal to display
        information is called Hybrid computer.Information in continuous formInformation depends on
        and displayed in the form ofoperating mode of curves. It is used to measurecomputer. It can display
        continuous physical quantityinformation in discrete like as current flow,and continuous form
        temperature, blood pressure,because for digital heart beats.processing and next part is for analog
On the basis of Size: Super, Mainframe, Mini and Microcomputer:
Super Computer: Multi-user, multiprocessor large computer of very high efficiency and storing capacity
is called supercomputer able to solve very difficult and complex problem within a nano seconds. A
number of RISC (Reduced Instruction Set Computer) processors are used.
It is used in :
(i) Used to forecast the Weather and global climates
(ii) Used in military research and defense systems
(iii) In automobile, aircraft, and space craft designing
(iv) In encrypting and decoding sensitive intelligence information
(v) Used in seismography, plasma and nuclear research.
(vi) Protein folding analysis
(vii) Study of DNA structure and gene engineering
(viii) Digital film rendering
Example: C-DAC (Center for Development of Advanced Computer) of India has developed PARAM
series of Super Computer.
ANURAG is also Indian Super Computer. Other Super computers are CRAY XMP/14, CDC-205 etc. Mr.
Seymour Cray was a pioneer person in the field of supercomputer production. He had developed the
first super computer Cray-1 in 1976.
Mainframe Computer: It is also very powerful multi-user computer used in large business
organizations, examination department of examinations, industries and defense to process data of
complex nature. It can response several hundred request very quickly. It uses several CPU for data
More than 100 users can use mainframe computer at a time because it works on time sharing mode.
IBM built the first Mainframe Computer, System/ 360, in 1964.
Example: IBM S/390, IBM S/709, ICL 39, CDC 6600
It is used in :
Government and civilian
Credit card processing
Business data processing in large organization
Air traffic control system
Industrial design
Minicomputer: Minicomputers are larger and more powerful than most microcomputers but are
smaller and less powerful than most large mainframe computer systems. However, this is not a precise
destination. High-end models of microcomputer systems (super micros) are more powerful than some
midrange computers.
It is also multi-user computer and supports more than dozens of people at a time. It is costlier than
microcomputer. It is also used in university, large business organizations to process complex data. It is
also used in scientific research, instrumentation system, engineering analysis, and industrial process
monitoring and control.
Example: PDP-11, VAX etc.
Microcomputer: In 1976 the first personal Computer – Apple-1, Apple computer is designed. In 1981
August, IBM had announced the IBM 5150 PC, in New York. Now a day mostly used computers are
microcomputers. It is called Home PC or Personal computer (PC) because it is a single user computer.
It supports many higher level languages, multimedia, graphics, 3D graphics and games.
It is popular among students, professionals and home wives due to small size, low price, and low
maintenance cost and easy in operation. The Internet is popular due to PC and it is available for all
income groups. The American weekly magazine regarded it “Machine of year” in 1982 when IBM
lunched PC in market first time. The first IBM PC was equipped with following components:
Intel 8088 Processor of 4.77 MHZ
64 KB RAM (expandable to 256 KB)
5.25″ floppy drive (160KB)
Example: IBM PCs, Apple Mac, IBM PS/2 etc.
Laptop and Palmtop Computers
These handheld computers are not replacements for desktop computers. Desktop computers continue
to perform major processing functions, while palmtops are satellite for quick and mobile information
access and communication. Computers are small, portable, less power consuming and equipped with
all the facilities of modern PC. These computers can be operated by battery. These computers have no
enough storing capacities like as desktop computers, but not less in other facilities. It has CD drive,
floppy drive, modem and other input/output ports.
The idea of laptop computer was originated by Alan Kay of Xerox Palo Alto Research Center in 1970
and named to notebook like computer as Dynabook, but first Laptop was designed in 1979 by William
Moggridge of Grid System Crops. In 1983, Gavilan produced a laptop computer with 64 Kilobyte
memory, MS-DOS operating system, touchpad mouse, portable printer of weight 9Ib.
Learning and self-improvement are critical to educational leaders. Enormous amounts of information
are created constantly, and the lifelong learner needs to have timely access to it. Web pages and other
digital documents can be put on palmtop computers for enrichment. Palmtop computers are boon for
remote area where there is no electricity facilities available.
The higher authorities, social workers, researcher working in remote rural area get more benefits by
palmtop or laptop computers. The desktop is your personal computer seated at the top of your desk,
laptop has no problem on your lap, and palmtop is happy in your palm.