Computer Histroy

A computer is a machine for manipulating data according to a list of instructions.
Computers take numerous physical forms. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers. [1] Today, computers can be made small enough to fit into a wrist watch and be powered from a watch battery. Society has come to recognize personal computers and their portable equivalent, the laptop computer, as icons of the information age; they are what most people think of as "a computer". However, the most common form of computer in use today is by far the embedded computer. Embedded computers are small, simple devices that are often used to control other devices—for example, they may be found in machines ranging from fighter aircraft to industrial robots, digital cameras, and even children's toys.

The ability to store and execute programs makes computers extremely versatile and distinguishes them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: Any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, computers with capability and complexity ranging from that of a personal digital assistant to a supercomputer are all able to perform the same computational tasks as long as time and storage capacity are not considerations.
http://en.wikipedia.org/wiki/Computer

Hardware History Overview Modern computing can probably be traced back to the 'Harvard Mk I' and Colossus (both of 1943). Colossus was an electronic computer built in Britain at the end 1943 and designed to crack the German coding system - Lorenz cipher. The 'Harvard Mk I' was a more general purpose electro-mechanical programmable computer built at Harvard University with backing from IBM. These computers were among the first of the 'first generation' computers. First generation computers were normally based around wired circuits containing vacuum valves and used punched cards as the main (non-volatile) storage medium. Another general purpose computer of this era was 'ENIAC' (Electronic Numerical Integrator and Computer) which was completed in 1946. It was typical of first generation computers, it weighed 30 tonnes contained 18,000 electronic valves and consumed around 25KW of electrical power. It was, however, capable of an amazing 100,000 calculations a second.
The next major step in the history of computing was the invention of the transistor in 1947. This replaced the inefficient valves with a much smaller and more reliable component. Transistorised computers are normally referred to as 'Second Generation' and dominated the late 1950s and early 1960s. Despite using transistors and printed circuits these computers were still bulky and strictly the domain of Universities and governments.
The explosion in the use of computers began with 'Third Generation' computers. These relied Jack St. Claire Kilby's invention - the integrated circuit or microchip; the first integrated circuit was produced in September 1958 but computers using them didn't begin to appear until 1963. While large 'mainframes' such as the I.B.M. 360 increased storage and processing capabilities further, the integrated circuit allowed the development of Minicomputers that began to bring computing into many smaller businesses. Large scale integration of circuits led to the development of very small processing units, an early example of this is the processor used for analyising flight data in the US Navy's F14A `TomCat' fighter jet. This processor was developed by Steve Geller, Ray Holt and a team from AiResearch and American Microsystems.
On November 15th, 1971, Intel released the world's first commercial microprocessor, the 4004. Fourth generation computers were developed, using a microprocessor to locate much of the computer's processing abilities on a single (small) chip. Coupled with one of Intel's inventions - the RAM chip (Kilobits of memory on a single chip) - the microprocessor allowed fourth generation computers to be even smaller and faster than ever before. The 4004 was only capable of 60,000 instructions per second, but later processors (such as the 8086 that all of Intel's processors for the IBM PC and compatibles is based) brought ever increasing speed and power to the computers. Supercomputers of the era were immensely powerful, like the Cray-1 which could calculate 150 million floating point operations per second. The microprocessor allowed the development of microcomputers, personal computers that were small and cheap enough to be available to ordinary people. The first such personal computer was the MITS Altair 8800, released at the end of 1974, but it was followed by computers such as the Apple I & II, Commodore PET and eventually the original IBM PC in 1981.
Although processing power and storage capacities have increased beyond all recognition since the 1970s the underlying technology of LSI (large scale integration) or VLSI (very large scale integration) microchips has remained basically the same, so it is widely regarded that most of today's computers still belong to the fourth generation.