• A computer is an automatic machine made up of electronic and electro mechanical devices that processed data under program control to generate meaningful information with speed and accuracy.
• It can perform long and complex calculations, and analyse complex scientific or mathematical data. Computer hardware includes the physical computer and its peripheral components, is given. Input, output and storage devices, along with other types of computers, are identified and explained.
• Data are usually represented in a computer using the numbers, alphabets-A to Z symbols, graphs and images.
• This form of representation is used to formulate problem and fed to the computer.
• The processed output is required in the same form. This form representation is called external data representation.
• However the computer can understand data strings of binary digits, or bits.
• A bit is a smallest unit of data in a computer. It is represented a 1 or a 0.
• A unique combination of eight bits referred to as a byte, represents each character in a computer.
• Two most important characteristics of hardware in a computer are speed and size.
• Computer processing time is measured in millions of a second; the instructions processed per second is expressed in MIPS (million instruction per second).

Analog Computer
Analog computers are used to process continuous data. Analog computers represent variables physical quantities. Thus any computer which solve problem translating physical conditions such as flow, temperature, pressure, angular position or voltage into related mechanical or electrical related circuits as an analog for the physical phenomenon being investigated in general it is a computer which uses an analog quantity and produces analog values as output. Thus an analog computer measures continuously. Analog computers are very much speedy. They produce their results very fast. But their results are approximately correct. All the analog computers are
special purpose computers.
 Digital Computer.
Digital computer represents physical quantities with the help of digits or numbers. These numbers are used to perform Arithmetic calculations and also make logical decision to reach a conclusion, depending on, the data they receive from the user. Digital computer classified into 3 types. These are:
• Main Frame Computer
The most expensive, largest and the most quickest or speedy computer are called mainframe computers. These computers are used in large companies, factories, organizations etc. the mainframe computers are the most expensive computers; they cost more than 20 million rupees.
In these computers 150 users are able to work on one C.P.U. The mainframes are able to process 1 to 8 bits at a time. They have several hundreds of megabytes of primary storage and operate at a speed measured in nano second.
• Mini Computer

Mini computers are smaller than mainframes, both in size and other facilities such as speed, storage capacity and other services. They are versatile that they can be fitted where ever they are needed. Their speeds are rated between one and fifty million instructions per second (MIPS).
They have primary storage in hundred to three hundred megabytes range with direct access storage device.
• Micro Computer
These are the smallest range of computers. They were introduced in the early 70’s having less storing space and processing speed. Micro computers of today’s are equivalent to the mini computers of yesterday in terms of performing and processing. They are also called “computer of a chip” because its entire circuitry is contained in one tiny chip. The micro computers have a wide range of applications including uses as portable computer that can be plugged into any wall.
 Hybrid Computer
Various specifically designed computers are with both digital and analog characteristics combining the advantages of analog and digital computers when working as a system. Hybrid computers are being used extensively in process control system where it is necessary to have a close representation with the physical world. The hybrid system provides the good precision that can be attained with analog computers and the greater control that is possible with digital computers, plus the ability to accept the input data in either form.

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