The growth of computers was very rapid and it resulted in complicated computer systems. So, the luxuriously grown computers can be classified variously basing on varied criteria.
They can be classified on the following:
I) DESIGN II) SIZE AND CAPACITY III) PURPOSE IV) EVOLUTION V) NUMBER OF USERS
I) DESIGN:
Based on the design of the computer technology, computers can be classified into 3 categories.
a) ANALOG COMPUTERS b) DIGITAL COMPUTERS c) HYBRID COMPUTERS
a) ANALOG COMPUTERS:
The computers which are based on continuous physical variation of voltage to process input are called analog computers. These are mostly used in scientific and engineering fields, as, in these fields machines are required to measure and control certain processes. An analog computer can be used only for the purpose for which it was developed or designed.
b) DIGITAL COMPUTERS:
Computers which accept process and output data in the form of characters are called as “digital computers”. Digital computers accept data in the form of alphabet, digits and process the same as per pre-determined instructions (programs).
c) HYBRID COMPUTERS:
The computers which process data by means of both counting and measuring input values are called hybrid computers. These computers combine the functions of both digital and analog computers. They accept continuously varying input and convert it into definite voltage to represent digital data.
II) SIZE AND CAPACITY:
Based on size and capacity, computers can be classified into following kinds.
a) TINY COMPUTERS (MICROCONTROLLERS)
b) SMALL COMPUTERS (MICRO COMPUTERS)
c) MEDIUM COMPUTERS (MINI/MIDRANGE COMPUTERS)
d) LARGE (MAINFRAMES COMPUTERS)
e) SUPERLARGE (SUPERCOMPUTERS)
a) TINY COMPUTERS (MICROCONTROLLERS) :
MICROCONTROLLER:
Microcontrollers also called computers are the tiny specialized microprocessors installed in “smart” appliances and automobiles. These microcontrollers enable microwave ovens for example to store data about how long to cook your potatoes and at what temperature.
b) SMALL COMPUTERS (MICRO COMPUTERS)
MICROCOMUTERS:
Microcomputers are small computers that can fit on or beside a desk or are portable. Microcomputers are considered to be of two types.
i) PERSONAL COMPUTER (PCs):
Personal Computers Are Desktop, Tower Or Portable (Laptops, Note Book, Sub Note Book, Pocket PCS (Electronic Organizers, Palmtop Computers,Pen Computers, Personal Digital Assistants (PDA))) Computers That Can Run Easy To Use Programs Such As Word Processing Or Spreadsheets.
ii) WORKSTATIONS:
Workstations were sophisticated machines that fit on a desk, cost many that thousands of dollars and were used mainly by engineers and scientists for technical purposes.
c) MEDIUM COMPUTERS (MINI/MIDRANGE COMPUTERS)
MINI/MIDRANGE COMPUTERS:
Minicomputers are machines midway in cost and capability between micro computers and mainframes. They can be used as single-user workstations. When used in a system tied by network to several hundred terminals for many users they are known as midrange computers. The Mini Computer over laps with other categories of computers. A low-end mini computer may be about as powerful as a high-end microcomputer and cost about the same. A high-end minicomputer may equal a low-end mainframe.
Minicomputers have been used to serve the needs of medium-size companies or of departments within larger companies often for accounting or design and manufacturing (computer aided design (CAD)/ CAM). Now many minicomputers are being replaced by groups of PCS and workstations in networks.
d) LARGE (MAINFRAMES COMPUTERS):
MAINFRAMES COMPUTERS:
The large computers called mainframes are the oldest category of computer system. The word “mainframe” probably comes from the metal frames, housed in cabinets on which manufacturers mounted the computer’s electronic circuit.
Occupying specially wired, air-conditioned rooms and capable of great processing speeds and data storage, mainframes are generally have been water or air-cooled computers that are about the size of a jeep and that range in price from $50,000 to $5 million. Such machines are typically operated by professional programmers and technicians in a centrally managed department within a large company.
EXAMPLE:
Banks, insurance companies and airlines which handle millions of transactions.
Federal aviation administration flight controllers are still using 1960s-era mainframes –Univac computers, which are no longer made to keep air traffic safe.
Mainframes manufacturers will probably promote new user for their equipment, there appear to be three trends:
i) Old mainframes will be kept for some purposes.
ii) Networks of smaller computers will grow.
ii) Mainframes are being re-invented.
e) SUPERLARGE (SUPERCOMPUTERS):
SUPERCOMPUTERS:
Typically priced from $2, 25,000 to over $30 million super computers are high-capacity machines that require special air-conditioned rooms and are the fastest calculating devices ever invented.
The most powerful computer, Janus Located At The Sandia National Laboratories In Albuquerque, New Mexico And Built By Intel, enables scientists to simulate the explosion of a nuclear bomb.
New communications lines have made possible super computing power that is truly awesome. In 1995 the national science foundation and MCI communications, the nation’s no.2 long distance provider, established a giant, 14,000 mile network called the very-high-performance backbone network service (VBNS) which links the five most important concentrations of supercomputers into what they called a new internet. Each of these locations has more than one supercomputer (Cornell) and Champaign Urbana has six each). With this arrangement a scientist sitting at a terminal or workstation anywhere in the country could have access to all the power of these fast machines simultaneously. At present this new internet is used only by an elite group of scientists for extremely complex projects (such as studies of weather turbulence) but it may one day be available to the public.
III) PURPOSE:
BASED ON PURPOSE THERE ARE OF TWO TYPES:
i) GENERAL PURPOSE COMPUTERS:
The digital computers which can be used to process data of various types are called general purpose computers.
ii) SPECIAL PURPOSE COMPUTERS:
The Analog Computers which are designed to undertake only specific processing are called special purpose computers. These computers are generally used in manufacturing, medicine, space technology and such other scientific and engineering fields. There are some digital computers which support only word processing. Such computers are also called dedicated computers.
IV) EVOLUTION:
The present shapes of computers are the result of innumerable experiments in the course of which the computers took various forms and sizes. Based on the course of their development, they can be again classified into the following types:
i) FIRST GENERATION COMPUTERS:
The computers which were developed in 1950s and which made use of vacuum tubes are called first generation computers. These occupied very large space and produced great deal of heat. They were also costly and their maintenance was expensive.
EXAMPLE: UNIVAC
ii) SECOND GENERATION COMPUTERS:
The computers which were developed in late 1950s consisting of transistors in place of vacuum tubes to contain and process data are called second generation computers. The transistors were very small. So these computers occupied less space and consumed less power. They produced less heat also. Needless to say, they were less expensive than the first generation computers.
iii) THIRD GENERATION COMPUTERS:
1960s saw the emergence of third generation computers. These were based on the possibility of replacing transistors by tiny electronic circuits. Circuits in large numbers could be integrated and arranged on small silicon plates called chips which were used in the computers. These computers which used integrated circuits are called third generation computers. Circuits which are used to represent information are very small and very close to one another. This enables these computers to process information at a very great speed of micro and nano seconds. These consumed less electricity and produced less heat. The most important feature of these computers is their compactness. They were very small in size.
iv) FOURTH GENERATION COMPUTERS:
These computers used the same chips which were used in the manufacture of third generation computers. But the chips used in fourth generation computers have very large scale integration of circuits and therefore these chips were more efficient and capable of processing more data. All the computers which used chips having very large scale integration of circuits can be categorized as fourth generation computers.
v) FIFTH GENERATION COMPUTERS:
In technology, the fifth generation computers are slightly more advanced than fourth generation computers. These computers possess the following additional capabilities:
a) Through Advanced Software, The Computers Can Be Put To Greater Use.
b) They Can Solve Problems of Greater Complexity and Variety.
c) They Can Undertake Problems Requiring Artificial Intelligence and Therefore They Will Be More User-friendly.
V) NUMBER OF USERS:
Based on usage of central processing unit:
There Are Of Two Types
i) SINGLE USER SYSTEMS:
A computer which can be used by a single person at a time is called single user computer system. Most of micro computers fall under this category.
ii) MULTI-USER SYSTEMS:
Computers which can be simultaneously used by two or more persons are called multi-user computers. In this system, a single computer is connected to a number of terminals through which many users can use it.
In fact, a single computer can be used both as single or multi-user system depending on its design and mostly on the type of operating being used.