The term Computer, originally meant a person capable of performing numerical calculations with the help of a mechanical computing device. The evolution of computers started way back in the late 1930s. Binary arithmetic is at the core of the computers of all times. History of computers dates back to the invention of a

mechanical adding machine in 1642. ABACUS, an early computing tool, invention of logarithm by John Napier and the invention of slide rules by William Oughtred were significant events in the evolution of computers from these early computing devices.

In the evolution of computers their first generation was characterized by the use of vacuum tubes. These computers were expensive and bulky. They used machine language for computing and could solve just one problem at a time. They did not support multitasking.

• It was in 1937 that John V. Atanasoff devised the first digital electronic computer. Atanasoff and Clifford Berry came up with the ABC prototype in the November of 1939. Its computations were based on a vacuum tube and it used regenerative capacitor memory.
• Konrad Zuse’s electromechanical ‘Z Machines’, especially the Z3 of 1941 was a notable achievement in the evolution of computers. It was the first machine to include binary and floating-point arithmetic and a considerable amount of programmability. In 1998, since it was proved to be Turing complete, it is regarded as world’s first operational computer.
• In 1943, the Colossus was secretly designed at Bletchley Park, Britain to decode German messages. The Harvard Mark I of 1944 was a large-scale electromechanical computer with less programmability. It was another step forward in the evolution of computers.
• The U.S. Army's Ballistics Research Laboratory came up with the Electronic Numerical Integrator And Computer (ENIAC) in 1946. It came to be known as the first general purpose electronic computer. However it was required to be rewired to change it’s programming thus making its architecture inflexible. Developers of ENIAC realized the flaws in the architecture and developed a better architecture. It was known as the stored program architecture or von Neumann Architecture. It got its name after John von Neumann, who for the first time described the architecture in 1945. All the projects of developing computers taken up thereafter have been using the von Neumann Architecture. All the computers use a ‘stored program architecture’, which is now a part of the definition of the word ‘computer’.
The U.S. National Bureau of Standards came up with Standards Electronic/Eastern Automatic Computer (SEAC) in 1950. Diodes handled all the logic making it the first computer to base its logic on solid devices. IBM announced the IBM 702 Electronic Data Processing Machine in 1953. It was developed for business use and could address scientific and engineering applications. Till the 1950s all computers that were used were vacuum tube based.

In the 1960s, transistor based computers replaced vacuum tubes. Transistors made computers smaller and cheaper. They made computers energy efficient. But transistors were responsible for the emission of large amounts of heat from the computer. Due to this computers were subject to damage. The use of transistors marked the second generation of computers. Computers belonging to this generation used punched cards for input. They used assembly language.

• Stanford Research Institute brought about ERMA, Electronic Recording Machine Accounting Project, which dealt with automation of the process of bookkeeping in banking.
• In 1959, General Electric Corporation delivered its ERMA computing system to the Bank of America in California.

The use of Integrated circuits ushered in the third generation of computers. Small transistors placed on silicon chips, called semi conductors. This increased the speed and efficiency of computers. Operating systems were the human interface to computing operations and keyboards and monitors became the input-output devices.

• In 1968, DEC launched the first mini computer called the PDP-8.
• In 1969, the development of ARPANET began with the financial backing of the Department Of Defense.

Thousands of integrated circuits placed onto a silicon chip made up a microprocessor. Introduction of microprocessors was the hallmark of fourth generation computers.

• Intel produced large-scale integration circuits in 1971. During the same year, Micro Computer came up with microprocessor and Ted Hoff, working for Intel introduced 4-bit 4004.
• In 1972, Intel introduced the 8080 microprocessors.
• In 1974, Xerox came up with Alto workstation at PARC. It consisted of a monitor, a graphical interface, a mouse, and an Ethernet card for networking.
• Apple Computer brought about the Macintosh personal computer January 24 1984.

The fifth generation computers are under development. They are going to be based on principles of artificial intelligence and natural language recognition. Developers are aiming at computers capable of organizing themselves. The evolution of computers continues.