Some Important Definition.

Input Devices:
these devies that can be used to insert information / data into a computer and other devices connected to the computer. The example of input devices are mouse, keyboard, mouse and others devices.
Output Devices:
these devices that can be used to show any result of input devices is known as output.The example of output devices are printer, scanner,speaker and other devices.

Hardware:
hardware is belong to output devies. the physical devices of any machine such as computer is known as Hardware.the example of hardware is Motherboard, RAM, ROM, Power-Supply and others Part of any Computer.

Software:
The collection of data or information is known as program and the collection of program is called Software. The logical system insert the computer is known as software. there are 2 types of software

•  System Software.
•  Application Software.

System Software:
Those programs that are spatially designed to operate and control the hardware and to provide a platform for the execution of application software.the example of system software is operating system, windows 7, windows 8, MAC, linux and other operating systems.
Application Software:
The application program is the set of computer software which causes a computer to execute beyond the useful operation of the computer itself tasks. A specific example of such software is called a software program, application. Those program which are designed for any perpose just suppose anti-viruses, security perpose, marketing purpose and other purpose.

Types of Computers

Computer consist of 3 main types:

•  Analog Computer.
•  Digital Computer.
•  Hybrid Computer.

Analog Computer:

An analog computer is a form of computer that uses continuous modifiable aspects of physical phenomena such as electrical quantities, mechanical, hydraulic or model the problem is solved.Computer wherein variable physical quantity, such as electrical potential, the fluid pressure, or mechanical motion, are used to represent (by analogy) the quantities in the problem to be solved. In contrast, digital computers are symbolically varying amounts that their digital values ​​change. They have been widely used in simulation of the operation of aircraft, nuclear power plants, and industrial chemical processes.The analog system is established based on initial conditions and then allowed to change freely.As an analog computer is not using discrete values, but rather continuous values ​​, the process can not be reliably repeated with exact equivalence , as they can with Turing machines . Analog computers do not suffer from the quantization noise inherent in digital computers, but they are limited instead by the analog noise.
Analog computers have been widely used in industrial and scientific applications where digital computers of the time did not have a sufficient return. The answers to this problem are obtained by measuring the variables of the analog model. Analog computers are particularly well suited to the simulation of dynamical systems, these simulations can be performed in real time or at rates significantly accelerated, allowing experimentation by performing numerous tests with different variables. Analog computers can have a wide range of complexity. Slide rules and charts are the simplest , while control computers naval artillery and large digital computers/analog hybrids are among the most complex. Systems process control and relay protection used analog computing to perform control and protection functions.
Digital Computer.
Computer capable of solving problems by processing information expressed in digits. By manipulating combinations of  digits(0 to 9) and alphabets (Ato Z). The performance of Digital Computers is good as Analog Computers .Digital computers can perform mathematical calculations,  monitor industrial and other processes, organize and analyze data and simulate dynamic systems such as global weather, calculator, mobile phones and much more.
Hybrid Computer.
the combination of analog computers and digital computers is known as Hybrid Computers. Hybrid computers is used in Petrol Pumps, Hospitals even homes. The performance of Hybrid computers is very good than Analog computers, and Digital Computers.

Definition Of Computer

The term computer can logically be applied to any type of computing device. In the simplest, one can say that all devcie that calculates a computer. However, in common usage, the term is used for an automatic electronic digital computer. Normally this computer has at least a keyboard, monitor and processor.
The computer is defined in many different words a few definations are listed below:

•  Computer is a machine that accepts data, processing it and gives output.
•  A computer is a devie capable of accepting data, applying described processes to data and supplying result of these processes.
•  Computer calculation deviated automatic electronic that can process data in a predefined manner and produces the desired results.