A computer basically is an electrical machine which receives data from users, processes the data and operations on it and generates the output according to input. Computer means to Calculate. Generall purpose to control raw facts (data) according to a set of instructions that are given by users. A computer can not only store and process data but also retrieves data i.e, take out data from its memory or storage as when desired thus, the computer is a general language that refers to an electronic data processing machine used for a wide range of activities.Important terms in the computer:Raw facts are known as data.meaningful data usually say information that we give to the computer.those commands that tell the computer what to do, these commands are known as instructions.set of instructions are known as a program.those things in the computer we usually touch and feel like keyboard, mouse etc. are known as hardware. those things in the computer we do not touch but see in the form of data and information like programs are known as software.Types of computer Basically, two types of computers based on working:1. Analog computersAnalog computers handled or process information which is of a physical nature for example temperature pressure. these are based on the measuring of analog or equivalent physical value.2.Digital computersDigital computer process information essentially in binary or two-state form namely zero and one. whenever we talk and read about computer mostly refer to the digital type of electronic devices.Note: Hybrid computer is also a type of computer, this is the combination of Analog computers and Digital computers. These computer used by hospitals like ECG and DIALYSIS.Digital computer also divided into four categories based on size: # Microcomputer (small size) People use desktop computers or personal computers but they do not know what type of digital computer, it is microcomputer because these computers are the least powerful, most widely used and fastest growing. They also called portable computers because they carry anywhere. It includes a microprocessor, memory, and minimal input/output (I/O) circuitry mounted on a single printed circuit board. Microcomputers became popular in the 1970s and 1980s with the arrival of increasingly powerful microprocessors. Examples of microcomputers are pc, notebook, tablet computer etc.# Minicomputer (medium size)Minicomputers smaller in size, faster, cheaper than mainframe computers. It was developed in the mid-1960s and designed to carry out some specific tasks, like engineering and computer-aided design (CAD) calculations. But today they are used as a server.Minicomputers are IBM-17, DEC PDP-11 etc.#Mainframe computer (large size)Mainframe (Meaning big iron ) computers have large internal memory storage and comprehensive range of software. They are mostly used for business work and a large amount of data processing. They are bigger in size and have better processing power compare to others computer like microcomputer, minicomputer, pc. It has the ability to handle a large amount of input and output so give special importance or value.Their high stability and reliability enable these machines to run without a break in continuity for decades and more secure than others computers.Modern mainframes have the ability to run the different operating system at the same time due to this technique allow applications to run as if they were on physically different computers. Examples: IBM-370, IBM-S/390, UNIVAC-1110.#Super computer (very larger size)Supercomputers are fastest, most expensive machines, high processing speed, speed measured in FLOPS(Floating Point Operation Per Second) and high level of computing performance. Supercomputers were introduced in the 1960s. Supercomputers are used for higher calculation and intensive tasks such as weatherforesting, nuclear research, and scientific research laboratories. In November 2017, a general survey shows that world’s fastest computers mostly run Linux-based operating systems. CRAY-1 was the world’s first supercomputer introduced by Seymour R CRAY in 1976.Titan is the first supercomputer which is based on GPU System.Tianhe-2 is the world’s fastest supercomputer launched by China in 2013Siddhartha was the first computer developed in India.History of computerThe creation of computer does not take one day or one month, it takes a long period of time for the creation of computer. From many years these computers are developing step by step, abacus (first calculating machine ) to the analytical engine (first computer)and analytical engine to the supercomputer.Abacus was the first mechanical calculating device invented by China in the 16th century. It is used for addition and subtraction. Pascalinewasthe the first mechanical adding machine invented by Blaise Pascal in 1642. It performs addition and subtraction of two numbers.Analytical engine (1834-1837)was the first general purpose computer invented by Charles Babbage. It generally used for basic arithmetic operations.EDSAC (1946-1952)was the first computer which provides storage capacity invented by John von Neuman.IBM-650 was provided input /output units converting alphabetical and special characters to two-digit decimal code invented by IBM company in 1954.