Rise of the machines, south of Milton Keynes
Computers make a noise at TNMOC
Geek's Guide to Britain It’s the sounds that get you: wheels spinning, processors squeaking, the furious hammering of teleprinters, and some 1980s synth.
Yes, computers really were this noisy – something you forget in an era when even the benign tap of the keyboard is giving away to the silent swoosh of finger on glass.
I’m at The National Museum of Computing History (TNMOC) in Bletchley Park, near Milton Keynes, home to some of the oldest and rarest computers in the world. We have a working rebuild of WWII code breaker Colossus Mk II; schoolkids’ favourite the BBC Micro; and one of the NeXT workstations - created by Steve Jobs and his new company after he was booted from Apple - the machine picked by Tim Berners-Lee to help give birth to the worldwide web at CERN in the early 1990s.
It’s near the end of my two-and-a-half hour TNMOC tour when the crescendo of microprocessors, sound chips and external electro mechanic sounds from these and many more computers finally hits me.
I’m not alone in appreciating these sounds: professionals are on the case, too. DJ Pixelh8, AKA Matthew Applegate, in 2009 caught, sampled and remixed the sounds of TNMOC with Obsolete, an album celebrating the mathematics, logic, code-breaking and crypto work of the machines and TNMOC.
TNMOC is filled with noises because, unlike some museums that place artefacts behind glass, and even in contrast to other computer museums around the world, TNMOC’s objects work and TNMOC wants you – in most cases – to touch.
Spencer with Tunny, the replica of the machine that cracked the German high-command's Lorenz communications
It’s an appeal that transcends the generations, a fact attested to by increasing visitor numbers. Dads in their 40s, whose first computer was a ZX Spectrum, schoolkids getting their first taste of programming on a BBC Micro, pensioners of the WW2 code-breaking generation and others in between are being lured by TNMOC.
My guide for a two-hour TNMOC tour, Andrew Spencer, explains how it’s not only the well-known kit that people can't wait to play with. Normally, it’s the kids who love inputting their names into a lost classic Elliott 903 and have the Elliott’s chattering teletype punch out their names on paper tape. On one particular trip, though, it was a senior IT executive who took command and who printed out no less than eight tapes. “You have some people who have never experienced that,” Spencer recalls.
But this is modern, post-war stuff and our tour starts in Our Finest Hour: WWII, when the site TNMOC occupies was part of the UK Government’s Code and Cypher School at Bletchley Park. At its peak, 12,000 mathematicians, engineers, military personnel and other staff toiled in three shifts around the clock, seven days a week to crack the encrypted communications of Nazi Germany’s high command.
TNMOC occupies Block H of Bletchley Park, a squat and angular bunker-like building built in 1944 from reinforced concrete to withstand bombing to house six of Bletchley’s 10 Colossi. The other four were held in Block F, now demolished. Block F didn’t go without a fight: tearing down the concrete walls took the hapless contractor who was awarded the job six months, and cost him two of his precious three wrecking balls, on a job he reckoned would take three weeks.
Our tour begins in two galleries dedicated to the Tunny and Colossus, built to crack communications encrypted using the Germans’ Lorenz SZ42 cipher machine.
Lorenz messages were enciphered by adding a series of apparently randomly generated letters to each letter in the original message, with random letters generated by a fiendish combination of 12 rotors. To decrypt, the receiving Lorenz added exactly the same obscuring letters back to the cipher text, also using its 12 rotors. Messages were communicated in International Teleprinter Code, where each letter of the alphabet is represented by a series of five electrical impulses; Morse code was not used.
The Colossus Mk II rebuild: the spinning wheels of statistical attack
The Tunny was built by a team from the Post Office Research Station without ever seeing a Lorenz, having worked out the machines’ logical structure of circuits and rotors. Nobody actually knows for sure, but it is believed there were been between 15 and 20 Tunnies operating at Bletchley during WWII.
The Tunny produced the final decrypts, but that still left the job of working out the starting position of the Lorenz’s rotors – a process that was being done by hand and thus took several weeks. Work was started on a new machine that led to the Colossus Mk I and Colossus Mk II, which cut the job to six hours.
The secret? Thermionic valves, the forerunner to solid-state components such as transistors and diodes in today’s computers. Valves controlled a current in a vacuum-sealed glass tube and when arranged together could form a circuit. The Colossus program was entered through plug boards and switches, and the message was run on the tape across a series of wheels. The valves sped up the rate of numerical analysis on the messages.
Valves had been the idea of Tommy Flowers, an electrical engineer with the General Post Office (GPO), which ran the UK’s phone services. Flowers had been working with valves since 1934 and argued they possessed the necessary power and reliability. The first Colossus in 1943 used 1,500 valves; Colossus II in 1944 used 2,500 valves.
If you visit the museum, you won't be seeing the original Tunny and Colossus - they were destroyed after the war on the order of the top brass as Lorenz machines began falling into the hands of the Soviets. The machines on display are working rebuilds, constructed from scratch by volunteers working from a handful of old photos, circuit diagrams and – in the case of the Colossus Mk II – the memory of Flowers himself.
The Tunny is big, measuring 7.5ft high and 4ft wide and about one foot deep, but the Colossus is even bigger: 7.5ft high and 6ft deep and 15ft long. The Colossus Gallery housed Colossus machine number nine.
How did the Tunny and Colossus work?
Inside the machine
First, the teleprinter code came in over the air – that’s the wibbly wobbly high-frequency radio noise you’ll hear filling the air of the Tunny gallery when you take the tour. Back in the war, this noise was filtered and converted by hand to paper tape that was stuck together to make a loop that fed over a series of spinning wheels and was read optically.
The Colossi were programmed to conduct a statistical attack on the code to work out the probability of what each letter meant and thereby determine the Lorenz wheels’ start position. This attack was mounted using the valves chewing the algorithm they’d been fed.
The Elliott 903's boisterous teleprinter (centre) lures kids and senior IT execs
Listen carefully, and above the crazy whirling and reeling of wheels and whooshing of tape on the Colossus Mk II you can also detect a hypnotic tick, tick, tick as the wheels complete a revolution; they spin at 40 miles per hour, reading 5,000 characters per second. Colossus could read 10,000 characters a second, but at that speed the tape would break, so 5,000 was the limit. Each click is a single revolution, with each revolution a statistical attack on the message. So, what you’re hearing is computing in action.
Was it worth it? Colossus played a pivotal role in the D-Day invasion: signals between Hitler and Field Marshal Rommel were cracked using the Colossus Mk II to reveal Hitler had bought the Allies’ deception that the invasion of Northern Europe was coming to Calais in 1944; he overruled Rommel’s request to shift elite Panzer troops down to Normandy, a move that could have turned the invasion into another bloody defeat like the Gallipoli landings of World War One. The message was reviewed in Block D, at Bletchley Park by – we’re told – by "very senior members of command".
All told, TNMOC reckons 63 million characters of “high-grade” German communications were decrypted by 550 people on the 10 Colossus computers.
The atmosphere today in the Colossus gallery feels like some stately home filled with the sound of the mechanical ticking and gentle spinning of antique time pieces. However, it wasn’t like that when the Women’s Royal Naval Service (WRNS, colloquially known as Wrens) ran the machines. The noise was the same but the room was hot, humid and - occasionally - hazardous.
This gallery housed a single Colossus machine that was never turned off. The machine ran 24 hours a day and seven days a week because – Flowers believed – as long as the valves were left powered on, they could operate reliably for very long periods, especially if their heaters were run on a reduced current.
It’s assumed the room's doors remained shut and windows closed owing to the blanket of secrecy that smothered Bletchley, and also because of the night-time blackout that everybody had to observe during the war.
So solid: 20Kb of memory represented in metal mesh and 160,000 hand-made rings
That meant things got hot and humid. In true stiff upper lip fashion, the brass permitted the Wrens to remove their jackets and roll up their sleeves as a concession to these uncomfortable working conditions. They were the only Wrens allowed this level of undress - you can see them here.
Once a leak flooded the room housing Colossus No 9 with water, something that would have been dangerous to machine and the Wrens - for different reasons. This flood is believed to be the source of a persistent myth that water was poured on the floor to try to keep temperatures in the room down.
We leave the dedicated galleries and head to the post-war world, and run into more valves: 829 of them, to be precise. That tungsten-coloured glow represents the computing power running the world’s oldest working digital computer: the Harwell Dekatron Computer, or WITCH, recently rebooted following a four-year renovation.
The WITCH is really a 2.5-ton calculator that ate numbers and spat out answers to complex calculations for the Atomic Energy Research Establishment. It was meant to be more reliable than a team of mathematicians punching away at calculating devices.
Past the WITCH, things start to get more hands-on as we hit TNMOC’s three Elliotts, from Elliott Automation. The Elliotts mass produced in the 1960s and 1970s, with hundreds of units sold to business and academia, before the company was subsumed into ICL, GEC and British Aerospace through a series of deals.
The Elliotts boasted several unusual features and a number of firsts. The 803 is believed to be the first all-transistor computer used in the UK. It featured brand new magnetic cores for logic gates as well as for memory – of which it packed a mighty 20Kb. The 803 used magnetised 35mm film tape from Kodak for storage, and boasted the ability to plug into the mains power supply because, unlike its predecessors, it had dispensed with the need for a special power supply that juiced up the voltage.
Disc evolution: a 200MB slab of storage and its smaller descendants
It’s four cabinets’ worth of computer, with a reader and copier, an operator console – no monitor – and a plotter added to the set up in the 1960s. Next to the plotter lies a sheet of paper with a picture of a Kingfisher produced by the Elliott that looks like it was made on a kids’ spirograph - proof the Elliotts are still in use at TNMOC and evidence that a large number of Elliotts were used in design work, as well as for crunching numbers.
Peek inside a clear-sided cube on top of the 803 and you can see the 20Kb of solid-core memory: a matrix of crisscrossing wires intersected by 160,000 hand-made rings that changed to zero or one when a current was applied. Retrieving data meant scrolling through the Elliott’s 35mm magnetic storage tape, which could take up to 15 minutes.
Big disc, little disc
Despite this, the 803 was nowhere near powerful enough to run business-critical operations like wages, stores, and sales that big companies needed. This was handled by punch-card systems, of which one TNMOC room houses an example. It looks like the skeletal remains of a Terminator machine.
It’s the Elliott 903 where things get noisy. Elliott Automation added the paper tape reader and teletype to the 803. TNMOC has plugged in a monitor to this beast so you can view things electronically. The 903 adds a further 8K of memory while the processor makes a dry squeaky sound – like an old wheel in need of oiling.
The NeXT Cube: a lost classic from Steve Jobs' "black" phase
In an age when you didn't have monitors to see what was wrong, engineers added such sounds to determine how the machine was working, Spencer says. Engineers would listen for variations; silence, it seemed, was a sign things had gone wrong.
Opposite the Elliotts are 20 washing machine-shaped metal cabinets. This is an ICL 2966, the largest of TNMOC’s machines yet, with a mighty 7GB of disk storage. Machines like the 2966 were used in large public and private operations in the 1970s and 1980s. TNMOC’s beast ran billing, payroll, and general accounting for TARMAC Quarry Products in Wolverhampton between 1985 and 1999.
Storage in this room-sized squatter was tiny but performance was not: storage media consisted of massive ceramic discs covered with a magnetic coating and capable of holding 200MB each. Accessing a specific piece of data meant entering a query into a terminal that told you which disc held the data. The disc was then loaded into a reinforced cabinet, weighing two tons, and spun up to 1,000 RPM.
Both the drums and buildings hosting them had to be specially reinforced because they’d vibrate while running at full power, while the discs had a habit of breaking free. “One guy told me a story of it punching though the wall and into the River Thames outside,” Spencer says.
Arranged around the ICL beast and its 200MB disc is a display of storage media, showing how things have shrunk while capacity has grown.
The BBC Micro classroom, where many hack their first code
Now, though, we get personal as we enter a gallery of PCs from the 1980s: among them, Sinclair Spectrums, BBC Micros and Amstrads, and an IBM 5150 of the kind that became Time Magazine’s Person of the Year in 1981.
Here the sounds are more rounded than the metallic punching and dry squeaking of the Elliott, and they are ubiquitous and layered – an aural comment on the explosion in PC ownership during that decade and the sheer number of different types of PCs that were available. TNMOC seems to be piping in some soft '80s synth music, too. It’s here you can get hands-on and either relive old memories of key-tapping or show the kids how a program started by loading your code from a cassette tape.
TNMOC is a work in progress and the PC gallery is the last of its refurbished areas. In the unfinished room next door we find business computers in a holding pattern, waiting to be displayed properly.
If the gallery we left behind was for the consumer, this is all business. Among the machines here is a Xerox Star, whose program takes a full six hours to load. The machine is often left turned off, we’re told, because it's time to go home by the time it's up and running. A NeXT Cube workstation and a NeXT Station mini-computer complete the room’s artefacts. These are machines of legend, thrice blessed by the digital gods.
First, they were created by the hand of Steve Jobs at NeXT Computer, the company he founded after he was booted out of Apple in 1988 following a boardroom insurrection. Second, it was a NeXT that Tim Berners-Lee used at CERN to run the world’s first web browser – the Cube is one of CERN’s machines, but not, alas, the actual example used by Berners-Lee himself.
The NeXTSTEP object-oriented, multitasking operating system these machines run became the basis for Apple’s iOS when Apple bought NeXT – and Jobs – for $429m in 1996.
“People can use these machines,” Spencer tells me. “And people do use this one.”</
Alas, romance is kinder than history. Even in those heady days, people cooed over the NeXTs despite the fact they were ugly by the aesthetic of today’s silver Macs. Jobs, venerated today as an angel of design, was clearly going through his “black casing” phase. Also, few people could actually use a NeXT, as most applications were being written for Windows instead.
After the NeXT gallery you head into a room of twelve BBC Micros. Here, students and school pupils alike learn BASIC on one of the 1.5 million machines shipped shipped during the 1980s. Kids here hack a snake-like game.
“For most school students, it’s their first taste of programming,” Spencer tells us. Up to five groups a day are coming in to pound the Micros' chunky brown keys - and it’s not just kids: senior citizens from the University of the Third Age, ex-London-Underground IT staffers and Danish maths teachers have been filling in, too.
Back to the future inside TNMOC's PC gallery
There’s more at TNMOC, but our time’s up. There’s a room dedicated to ARM, which sprung out of BBC Micro-makers Acorn. Today Acorn dominates smart phones, air-traffic radar control, those Terminator-like hole-punch machines and a new software gallery.
On your way out we stop by the TNMOC shop and café, where you can pick up t-shirts, books, mugs and trinkets - including chunky-brown keys of cannibalized BBC Micro keyboards bearing your favourite letter or command. Cafe refreshments are solid - soft drinks and biscuits, teas and coffees from a machine.
Further afield is Milton Keynes, where you can catch up on shopping and the usual diversity of high-street refreshment. To the east are the spires and fens of Cambridge. If you want to linger overnight and recharge locally, there’s a handful of places to stay, including the Bletchley Park B&B. Again, Milton Keynes has more to choose from with the City Central B&B and Double Tree Milton Keynes. There are more choices in Cambridge
TNMOC is a museum that doesn’t stand still. It’s not just the exhibits that move, but the museum itself is in motion: after two skilled rebuilds (Tunny and Colossus) and one reconstruction (WITCH), a fourth project is now underway on EDSAC, built by Maurice Wilkes. EDSAC became the blueprint for the world’s first business computer, the Lyons Electronic Office (LEO) in 1951.
And while you can’t – and won’t - use these particular systems, TNMOC has an expanding culture of touch: at the time of writing this meant an exhibition on computer music where you can experiment with music software on PCs from the 1980s. TNMOC is running a series of interactive events for July, August and September that'll include a computer music weekend, Raspberry Pi and a games week.
The computers in your life might be getting quieter, but the computers from our past aren't staying quiet, it seems, thanks to TNMOC.
By train: between 30-50 minutes from London Euston to Bletchley. By car: between the A5 and A421, north of London.
Fee is £5 per person, with £2.50 concessions and no charge for children 12 and under. Entering Colossus and Tunny galleries only is £2, or £1 for concessions. TNMOC is free to members. Insight Guided Tours are priced at £5.50, with no concessions, and are only held on Tuesdays - booking is essential. The Colossus and Tunny galleries are open daily; the rest of TNMOC is open every Thursday, Saturday and Sunday afternoon from 1pm.
You can visit the TNMOC website here ®