About
The National Museum of Computing occupies Block H of Bletchley Park — the famous wartime Government Code and Cypher School in Buckinghamshire — though it operates as a completely independent institution from the Bletchley Park Trust and charges separate admission. Its focus is the complete history of computing, from the earliest electronic machines of the 1940s through to the personal computers of the 1980s and beyond, and it holds what is arguably the most important collection of historic computers in the world.
The museum's crown jewel is the world's only working rebuild of Colossus — the programmable electronic computer developed by Tommy Flowers at the Post Office Research Station in Dollis Hill between 1943 and 1944 to assist in breaking the Lorenz cipher messages of the German High Command. Colossus predated the American ENIAC by two years and was arguably the world's first programmable electronic digital computer, yet its existence was classified for decades after the war ended. The working rebuild, completed by a team of volunteers in 2007 after ten years of painstaking reconstruction from fragmentary documentation, is a monument to both the original genius of Flowers and his colleagues and the extraordinary skill of the rebuilders.
Beyond Colossus, the museum traces the full trajectory of computing history through an exceptional collection of working machines. The Harwell Dekatron WITCH — one of the oldest working digital computers in the world, patiently restored after decades in storage — stands alongside a reconstructed 1950s machine room complete with Elliott 803 computers, ICL mainframes from the 1960s and 1970s, and a succession of minicomputers from DEC, Data General, and British makers. A reconstructed 1980s classroom filled with BBC Micros evokes the era when a generation of British schoolchildren first encountered computing.
The museum's most important distinguishing characteristic is its commitment to keeping historic machines operational. Wherever possible, exhibits are demonstrated by expert volunteers — many of them retired engineers with direct experience of the machines on display — who explain what the computers did, how they worked, and why they mattered. The 1960s data centre, with its rows of full-height cabinets, tape drives, and punched-card readers, gives a visceral sense of scale and complexity that no static display could replicate.
Visitors should note that Bletchley Park Trust — the main Bletchley Park visitor attraction, focused on the wartime codebreaking story, Alan Turing, and the Enigma machine — requires separate admission and entrance. Many visitors buy combination tickets to see both on the same day. The National Museum of Computing is accessed through the Bletchley Park main entrance and is signposted to Block H on the right.
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Plan Your Visit
⏱️ Recommended Visit Duration
💡 Visitor Tips
- Plan a combined visit with Bletchley Park Trust, whose attraction immediately adjacent covers the Enigma cipher, Alan Turing, and wartime codebreaking in great depth — combined tickets are good value and the two institutions are strongly complementary.
- Ask at reception about Colossus demonstration times: the machine is run at specific times during opening hours and seeing it in operation — valves glowing, tape rattling at 5000 characters per second — is qualitatively different from seeing it static.
- The BBC Micro classroom computers are fully operational and visitors are actively encouraged to type in and run programs — there are BASIC program listings posted on the wall for those who want to try.
- Bletchley station is just 12 minutes' walk from the site entrance, making this an excellent day trip from London (45 minutes from Euston) or Birmingham (35 minutes from New Street) without a car.
- Allow at least two hours for TNMOC alone; if combining with Bletchley Park Trust, a full day is advisable. Both attractions have separate cafes and shops.
- The volunteer guides are a highlight of the visit — most have direct professional experience with the machines they are explaining, and their first-person accounts of working on 1960s mainframes or programming early minicomputers are irreplaceable.
- Check the events calendar: TNMOC holds special event days including 'Colossus Day' (marking the anniversary of Colossus entering service), gaming days for the personal computer collection, and heritage programming events.
Highlights
Colossus — The World's Only Working Rebuild
The centrepiece of the museum and one of the most important objects in the history of computing: a fully working rebuild of Colossus, the electronic codebreaking computer designed by Tommy Flowers in 1943-44. The original Colossus machines — ten were eventually built — were dismantled and their blueprints destroyed after the war to preserve secrecy; this rebuild was completed in 2007 by a team led by Tony Sale after ten years of painstaking reconstruction from fragmentary surviving documentation.
Watching Colossus run — its thyratron valves flickering, paper tape rattling at phenomenal speed — is to witness a moment of technological genius from eighty years ago replayed in real time.
Harwell Dekatron WITCH — One of the World's Oldest Working Computers
The WITCH (Wolverhampton Instrument for Teaching Computation from Harwell) is one of the oldest functional digital computers in existence. Originally built in 1951 at the Atomic Energy Research Establishment at Harwell, it uses Dekatron counting tubes — glass valves that visibly click round as they count — rather than electronic circuits, making it uniquely transparent and accessible to visitors.
Placed in storage for decades, WITCH was painstakingly restored and is now demonstrated regularly at the museum.
Watching it count, step by mechanical step, makes the birth of computing palpably comprehensible in a way that more modern technology cannot.
The 1980s BBC Micro Classroom
For visitors of a certain age, the reconstructed 1980s school classroom equipped with BBC Micro computers triggers pure nostalgia; for younger visitors, it is a window into the moment when computing became personal and democratic. The BBC Micro — designed by Acorn Computers for the BBC Computer Literacy Project launched in 1981 — put interactive computing into hundreds of thousands of British schools and homes and created a generation of programmers who went on to build the British games and software industries.
The machines in this classroom are operational and visitors are encouraged to load and run programs using cassette tape, exactly as schoolchildren did forty years ago.
The 1960s ICL Data Centre
A faithfully reconstructed 1960s commercial data centre, populated with full-height ICL mainframe cabinets, open-reel magnetic tape drives, punched card readers, and line printers, gives a visceral sense of the scale and complexity of early commercial computing. In the 1960s, a company's entire data processing operation might fill a room like this, require a specialist staff to operate, and cost as much as a factory.
The volunteers who operate this gallery, many of them former ICL or IBM engineers, bring it to life with demonstrations and first-hand accounts of what it was actually like to run a 1960s data centre.
Collections
The National Museum of Computing holds the most significant collection of historic computers in the United Kingdom and arguably in the world, spanning the period from 1940s valve machines through to the microcomputers of the 1980s. The collection's exceptional character derives from the museum's commitment to operational preservation: wherever possible, machines are maintained in working order and regularly demonstrated by knowledgeable volunteers.
Highlights include the unique Colossus rebuild, the Harwell WITCH, working ICL mainframes, Elliott minicomputers, and a comprehensive collection of 1980s home and personal computers.
The collection is supplemented by extensive software libraries, documentation, and peripheral equipment.
The Colossus Gallery
Permanent exhibition around the working Colossus rebuild, with full context on Tommy Flowers, the Lorenz cipher, and wartime codebreaking.
The 1960s Data Centre
Reconstructed commercial data centre of the 1960s with working ICL mainframes and peripherals.
The Personal Computer Revolution
Gallery tracing the development of personal computing from the mid-1970s through the 1980s.
Current Exhibitions
No current exhibitions. Please check the museum website for updates.