The principal characteristic of a computer are.

1. It responds to a specific set of instructions in a well-defined manner.
2. It can execute and prerecorded list of instructions.

All general-purpose computers need the following hardware components.

• Memory: Memory enables the computers to store, at least temporarily, data and programs.
• Mass storage device: Allows a computer to permanently retain large amounts of data. Common classic mass storage devices include disk drives and tape drives. The latest being the Hard Disks and USB mass storage devices.
• Input device: The most usual input devices are a keyboard and mouse. They are used to put in data and instructions to computer.
• Output device: The most usual output devices are display screens such as Monitor which are of several types now a days and a printer, or other device that lets us see what the computer has accomplished.
• Central processing unit (CPU): This can be called the heart or brain of the computer which actually executes the instructions.

However, they can be divided into several categories on the basis of cost and performance. We can classify the computers by their size and powers, though there is considerable overlap. On this basis computers may be a personal computer, a Laptop, a Palmtop, a Workstation, a Minicomputer, a Mainframe or a Supercomputer.

To work on a computer, we need an operating system. Operating system (OS) provides a set of functions needed and used by most applications, and provides the necessary linkages to control a computer's hardware.

The first computers did not have the operating systems and each program would have to have drivers for the video card, memory card, and other peripherals used. So, the evolution of the computer applications and their complexity led to the OS necessities. Operating System has the job of managing the computer hardware resources, and providing common services for execution of various application software. The operating system is the most important type of system software in a computer system. Without an operating system, a user cannot run an application program on their computer, unless the application program is self booting.

• The first integrated circuits contained only a few transistors and so were called "small-scale integration (SSI). They used circuits containing transistors numbering in the tens. They were very crucial in development of early computers. SSI was followed by introduction of the devices which contained hundreds of transistors on each chip, and so were called "medium-scale integration (MSI).
• They were attractive economically because which they cost little more systems to be produced using smaller circuit boards, less assembly work, and a number of other advantages. Next development was of LSI. The development of LSI was driven by economic factors and each chip comprised tens of thousands of transistors. It was in 1970s, when LSI started getting manufactured in huge quantities.
• LSI was followed by VLSI where "very large-scale integration"(VLSI), with hundreds of thousands of transistors, and beyond were used and still being developed. It was for the first time that a CPU was fabricated on a single integrated circuit, to create a microprocessor. In 1986, with the introduction of first one megabit RAM chips, more than one million transistors were integrated.
• Microprocessor chips produced in 1994 contained more than three million transistors. ULSI refer to "ultra-large scale integration" and correspond to more than 1 million of transistors. However there is no qualitative leap between VLSI and ULSI, hence normally in technical texts the "VLSI'' term cover ULSI.

A monolithic integrated circuit (IC) also known as microchip, silicon chip, computer chip or chip is basicaly a miniaturized electronic circuit that consists of mainly of semiconductor devices, as well as passive components. This circuit is manufactured in the surface of a thin substrate of semiconductor material. A hybrid integrated circuit is a miniaturized electronic circuit constructed of individual semiconductor devices, as well as passive components, bonded to a substrate or circuit board.

The integrated circuit was first conceived by a radar scientist, Geoffrey W.A. Dummer (born 1909), working for the royal radar establishment of the British ministry of defense, and published in Washington, D.C. on may 7, 1952. Dummer unsuccessfully attempted to build such a circuit in 1956.

The first integrated circuits were manufactured independently by two scientists; jack Kilby of Texas instruments filed a patent for a "solid circuit" made of germanium on February 6,1959. Kilby received patent 3261081, and U.S. patent 3434015. Robert Noyce of Fairchild semiconductor was awarded a patent for a more complex "Unitary circuit" made of silicon on April 25, 1961. Noyce credited Kurt lehovec isolation caused by the action of a biased p-n junction (the diode) as a key concept behind the IC.

Integrated circuits can be classified into analog, digital and mixed signal. Digital integrated circuits can contain anything from one to millions of logic gates, Flip-flops, multiplexers, and other circuits in a few square millimeters. The small size of these circuits allows high speed, low power dissipation, and reduced manufacturing cost compared with board-level integration. These digital ICs, typically microprocessors, DSPs, and micro controllers work using binary mathematics to process "zero" signals.

Analog ICs, such as sensors, power management circuits, and operational amplifiers, work by processing continuous signals. They perform functions like amplification, active filtering, demodulation, mixing, etc. analog ICs ease the burden on circuit designers by having expertly designed analog circuits available instead of designing a difficult analog circuit from scratch.

ICs can also combine analog and digital circuits on a single chip to create functions such as A/D converters and D/A converters. Such circuits offer smaller size and lower cost, but must carefully account for signal interference.

Introduction

We all know that a computer is an electric device and a programmable machine. The English mathematician, philosopher, inventor and mechanical engineer Charles Babbage (1791-1871) is known for originating the concept of a programmable computer and that is why he is called the "father of the computer".

Babbage was the first person who invented first mechanical computer that eventually led to more complex computers. He devised a plan for a stored-program mechanical computer, using data modeled after the punched card templates in industrial (jacquard) looms.

The first electronic digital computer was the ABC unit by John V. Atanasoff and Clifford Berry in 1940 at Iowa State University. Several of its ideas were incorporated into the ENIAC (Electronic Numerical Integrator And Computer) which ran from 1945-1955 and is considered the first functionally useful electronic digital computer.
Universal Automatic Computer (UNIVAC) was innovated in 1940s that led to the first commercially successful computer.

One of the earliest personal computers was the Intellect 4 by Intel, using their first commercially produced microprocessor –the four-bit 4004. The Altair built by MITS was another first commercially successful personal computer. Bill gates and Paul Allen wrote Microsoft's (then known as Microsoft) first software product for-"BASIC for the Altair''.

Then in 1983, came the TRS-80 that was Tandy Corporation's desktop microcomputer model line, which became famous as one of the trendiest home computers. Its TRS-80 Model 100 was an early portable computer introduced in 1983. It was one of the first notebook-style computers, or a prototype of a laptop, featuring a keyboard and LCD display, battery powered, in a package roughly the size and shape of notepad or large book. This model running on 4 AA batteries very soon got popular with newspaper reporters. Now writing stories from field was possible provided there was an internet connection.

The functioning of computers is primarily based on one thing that is their ability to determine whether a switch (gate) is open or closed. It can recognize whether it is on or off. But, it's the speed of this act which makes them so efficient. The speed which is now measured in megahertz and giga hertz trillions of cycles per second in the super computers. So, the data held in a computer in binary form, using the digits 0 and 1. By counting, comparing and manipulating these two digits in their various combinations according to a set of instructions held in its memory, computer is able to perform a variety of tasks.