Though in general we use digital computers, however, present day computers may be classified into three categories:
Analog Computers
Analog computers are computers which work on the basis of continuous measurement of physical quantities, e.g. pressure, voltage, current, temperature, current, length, etc.
We can quote a number of instruments that work on the principles of analog computers.
Digital Computers
Digital computers are computers which represent data in terms of discrete number and processes data using the standard arithmetic operations.
These computers directly operate on numbers and produce precise results. These are used in a unlimited number of applications.
The tasks that can be done on analog computers can also be done on digital computers while the reverse is not true.
To understand the calculations made by an analog computer, some mathematical background is necessary, whereas digital computer can be used and understood without much mathematical background.
Hybrid Computers
Design features of Analog and Digital computers can be combined to create a Hybrid Computer.
Such computers are used for special applications only. Examples of such computers include:
- Patient Monitoring System
- Electronic Calculating Scale
- Missile Guidance Computer
- Flight Simulators For Training Air-plane Pilots
- Petroleum Distillation Monitoring Systems
CLASSIFICATION OF DIGITAL COMPUTERS
There is a wide variety of computers in the market today which differ in terms of physical size, price, capacity, and performance.
The variety is so wide that it is sometimes difficult to see those elements that are shared by many computers and those elements that tend to differ among computers.
Depending upon their speed and memory size, computers are classified into following four main groups.
- Supercomputer
- Mainframe computer
- Mini computer
- Microcomputer
This classification implies differences between classes between in one or more characteristics.
In the 1960s, before the microcomputer, there was a clear-cut distinction between minicomputers and mainframes.
The most important characteristics that could be used to differentiate the two types of computers were :
- Speed
- Instruction sizes
- Number of CPU registers
- Word Length
- Main Memory Size
- Complexity of I/O modules
- Operating System Complexity
- Physical size
- Cost
- Virtual address space
- Secondary Memory Size
- Degree of Multiprogramming
Supercomputer
Supercomputer is the most powerful and fastest, and also very expensive. It was developed in 1980s.
It is used to process large amount of data and to solve the complicated scientific problems.
It can perform more than one trillions calculations per second. It has large number of processors connected parallel.
So parallel processing is done in this computer.
In a single supercomputer thousands of users can be connected at the same time and the supercomputer handles the work of each user separately.
Supercomputers are mainly used for
- To control industrial units.
Mainframe computer
The mainframe computer remains a distinct class of computers and is very powerful large general purpose computers.
Large organisations use mainframe computer.
Some of they like differences between the high end of mainframe class and high end the minicomputer.
Minicomputer
Minicomputers are faster and powerful more than microcomputers.
The word length of these computers are 32-bit or more.
A mini computer can support upto 64 or 100 terminals.
Mini Computers can support a greater veriety of fast peripheral devices.
Minicomputers are extensively used for multi-user and interactive applications in colleges, schools, organisations, government entities and industries.
The minicomputers are used in business, education and many other government departments.
Although some minicomputers are designed for a single user but most are designed to handle multiple terminals.
Minicomputers are commonly used as servers in network environment and hundreds of personal computers can be connected to the network with a minicomputer acting as server like mainframes, minicomputers are used as web servers.
Single user minicomputers are used for sophisticated design tasks.
The first minicomputer was introduced in the mid-1960s by Digital Equipment Corporation (DEC).
After this IBM Corporation (AS/400 computers) Data General Corporation and Prime Computer also designed the mini computers.
Microcomputers and its types
The microcomputers are also known as personal computers or simply PCs. Microprocessor is used in this type of computer.
These are very small in size and cost. The
IBM’s first microcomputer was designed in 1981 and was named as IBM-PC.
After this many computer hardware companies copied the design of IBM-PC.
The term “PC-compatible” refers any personal computer based on the original IBM personal computer design.
On the basis of cost and performance, personal computers can be classified as :
- Personal Computer (PC)
- Personal Computer with Extended Technology (PC/XT)
- Personal Computer with Advanced Technology (PC/AT)
- Super AT or Super Micro
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