History of Computers

Computers have been around for thousands of years, starting with the Abacus which was a mechanical device to help people add up more quickly, in fact the term computer used to refer to a person who carried out calculations. These were needed for working out the maths required in business, industry and science. What we now call a computer is just a device for working something out, usually mathematical in nature. The early ones were all mechanical in nature because electricity hadn't been discovered and this limited how fast they could work. Colossus

This page is concerned with the history of Electronic computers, so it really starts with Colossus. Colossus was the first electronic computer and was built at Bletchley Park in the UK to help decrypt ENIGMA and LORENZ communications during the Second World War.

A picture of Colossus is shown, left.

It was built using electronic valves, sometimes also called vacuum tubes. Valves are a type of electronic switch which can be turned on or off quickly. Despite the size of Colossus, it had a lot less computational power than one of today's mobile phones and used enough electricity to heat a house. Colossus was designed to perform just one job, decoding ENIGMA traffic, so it ran one program, this is unlike many computers today which are designed to run programs which can do many different jobs. Full size picture of Colossus:- colossus-mark1.jpg Because Colossus was developed in secret during the war, subsequent computers were based on different designs because only a few people knew of the existance of it. After the war had ended, it was broken up and destroyed to prevent the secrets within it becoming known. A replica of Colossus has been built at Bletchley Park, the original home of Colossus.

After the Second World War ended, the first computers started appearing for performing business and scientific calculations. ENIAC

Colossus was designed to do just one job and as such it could not be reprogrammed to do other tasks. The first computer designed to be reprogrammable was named ENIAC. It too used valves and took 160KW to run, approximately the same power as 50 houses.


In the 1950's computers started to be used for commercial purposes such as business accounts, but by today's standards they were very large, expensive to run and had limited storage. A typical 1950's computer would cost £1million and have 4k of memory to store information being processed, that's 4,000 bytes of memory.

One big improvement came with the use of magnetic tape and magnetic disks to store information, this allowed computers to process more information and access the information more quickly. In the picture on the right, you can see Magnetic Tape devices in the middle at the back, at the front on the left, you can see washing machine sized units which housed the Magnetic Disks.

These valve based computers were called the First Generation computers, from 1955, the Second Generation of computers were based on different technology. Valves were replaced with the newly invented Transistors which consumed a tiny amount of the power required by a valve and could work much faster and with greater reliability.

IBM 5150 With the launch of the first IBM personal computer, the desktop computer had arrived in a shape which most of us would recognise as a computer. Although the first model had only a green screen, 8Mhz CPU and 256K (not MegaBytes!), it had a keyboard and looked familiar.

Next page:- Types of Computer

c4c/history.txt · Last modified: 22/10/2014 10:20 by andrew