History of Computing

The National Museum of Computing at Bletchley Park, Milton Keynes, UK, houses the world's largest collection of functional historic computers, including the Colossus, the world’s first electronic computer, and the WITCH, the world's oldest working digital computer.

Colossus valve montageThe National Museum of Computing

Join this Expedition to follow the development of computing from the ultra-secret pioneering efforts of the 1940s through the large systems and mainframes of the 1950s, 60s and 70s, and the rise of personal computing in the 1980s and beyond.

Second World War Codebreaking

During the Second World War, both the Allied powers, including Great Britain, and the Axis powers, led by Nazi Germany, used encryption to keep communications related to the war effort secret from the enemy. 

The machines in this panorama were used by teams at Bletchley Park to help break encrypted Nazi radio messages. Decoding these messages was a challenging task that took a lot of people, some of the most advanced technologies of the day and, of course, time.

Radio receiving station

Radio receiving stations like this were set up all around the south coast of England to pick up and trace radio signals. If a signal came from Germany or anywhere occupied by the Nazis, it was recorded and sent to Bletchley Park.

Processing encrypted messages

At Bletchley Park, teams of women sat at machines like these. They typed out the encrypted messages relayed from the radio receiving stations, preparing them for the mathematicians who would try to break the codes. The teleprinter operators couldn’t make any mistakes!

Lorenz machine – Hitler’s secret encryption machine

Hitler, the German chancellor and leader of the Nazi Party, used a Lorenz machine like this to encrypt messages to his highest-level generals. Deciphering Lorenz-encoded messages was a major challenge for the cryptologists at Bletchley Park.


Mathematician Bill Tutte figured out how the Lorenz machine worked and made his own version, called Tunny. Tunny looks very different from the Lorenz machine, which Tutte had never seen, but the 2 machines work the same way.

Colossus – The World’s First Electronic Computer

Built by engineer Thomas ‘Tommy’ Flowers, Colossus was the world’s first programmable computer. The process of decoding messages with the Tunny machine required a lot of human input, and it was slow. Colossus was designed to mechanize that process.

Colossus enabled more messages to be deciphered and the whole codebreaking operation to be accelerated. The information gathered from the decrypted messages probably shortened the war by many months, saving tens of thousands of lives. 

How it works: paper tape

This paper tape contains the encrypted Nazi message. The tape spins quickly, and the computer reads it optically with a light, similarly to how CDs are read. Computers were programmed with paper tape until the 1980s.

How it works: teleprinter

Colossus was built about 30 years before graphic monitors, or screens, were invented. The results of calculations carried out by Colossus are not displayed but printed out by this teleprinter.

How it works: relays

A relay is an electrically driven mechanical switch. Relays were used in early telephone systems—Tommy Flowers was a telephone engineer—and computers to perform logical operations. Information about some key settings for Tunny were held in these relays. 

How it works: valves

Valves were used even before transistors to provide a very early form of computer memory. Data resulting from calculations performed by Colossus are stored in these valves. They get very hot, so this room is often very warm, especially in the summer.

The WITCH – The World’s Oldest Original Working Computer

The Harwell Dekatron, also known as the Wolverhampton Instrument for Teaching Computation from Harwell, or WITCH, is the world’s oldest working computer. Designed to automate the tedious work performed by mathematicians using mechanical calculators, it first ran in 1951.

It fell out of use in the early 1970s. In 2009, the National Museum of Computing took on the task of restoring the computer to working order. It was rebooted in 2012.


Dekatrons are gas-filled tubes that provide the computer’s RAM (Random Access Memory). A single dekatron stores up to 10 bits of data. The WITCH has less than ⅓ of a kilobyte of RAM—50 million times less than the average smartphone!

Input – paper tape

Like Colossus, the WITCH reads punched paper tape. This is how it is programmed. The computer’s tape readers are very slow—it would take 47 years to load the program for the game Call of Duty (which can’t actually be played on the WITCH!).

Control panel

The WITCH is like a giant, programmable calculator. It can add, subtract, multiply and divide. It was used to design the UK’s first nuclear power station in 1950. Because nuclear material is so dangerous, getting every calculation right was crucial.

Mechanical calculator

Before the WITCH, calculators were completely mechanical. They were slow and hard to use. To multiply, you put the number to be multiplied in at the top. Then you turn the handle the number of times by which you want to multiply. 

1960s and 1970s Large System Computers

Mainframes and large systems computers arrived in the 1950s. They were developed mainly for large organisations that required very large volumes of data processing, and they were BIG.

This collection at the National Museum of Computing represents computing in the 1960s and 1970s. Up until this time, computers were built to perform specific tasks. These new computers were programmable, which made them much more versatile.

Elliott 903

The Elliott 903 computer was developed in the mid-1960s. It doesn’t have a screen. Instead, results of calculations are printed out on a teleprinter. Smaller and faster than 1950s-era computers like the WITCH, it was still programmed using paper tape.

1960s data storage – hard disk

This is a hard disk, a form of data storage from the 1960s. It’s physically huge, but it can only hold 8 megabytes of data—that’s one photo and a very short sound clip. This disk cost £8000 when it was new!

Big washing machine-like boxes

This big box and its neighbors are part of a huge computer called the ICL 2966. These big machines functioned like today's USB drives. The ICL 2966 cost a whopping £3 million when it was new!

Elliott 803

This computer is an Elliott 803 that belonged to a woman named Dina St Johnston. Mrs St Johnston did all her own programming and put the computer to work for small businesses who couldn’t afford one of their own. This computer was very expensive, it cost as much as 10 family homes when it was new.

Personal Computing, 1980s to the Present Day

Beginning in the 1970s, computers were finally small and affordable enough that regular folks could own them and have them in their homes. The PC Gallery at the National Museum of Computing holds personal computers from the 1970s to the present.

Innovative designs on display include the BBC Micro, the Sinclair, the Amstrad and the Osbourne 1. The gallery also has timelines of the development of hardware and operating systems.

Computer games from the 1980s and 1990s

Once people had their own computers at home, they wanted to play games on them. Some famous early games include Space Invaders, Pac Man, Manic Miner, Pong, Lemmings and Paperboy. You can find emulators online to try these games at home.

Osbourne 1

The Osbourne 1 is often described as the world’s first laptop. In its day, it was also described as portable, but it weighs 11 kilograms (24.5 pounds), and that doesn’t include the optional external battery pack. 

iPhone 1 (first generation)

This is an original iPhone from 2007. It was the first in a new generation of smartphones, allowing people to carry a computer and internet access with them wherever they go. Now many people have smartphones.

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
Explore more
Google apps