Lately, [Ken Shirriff] has been on some of the most incredible hardware adventures. In his most recent undertaking we find [Ken] elbow-deep in the core memory of a 50-year-old machine, the IBM 1401. The computer wasn’t shut down before mains power was cut, and it has refused to boot ever since. The culprit is in the core memory support circuitry, and thanks to [Ken’s] wonderful storytelling we can travel along with him to repair an IBM 1401.
From a hardware standpoint core memory makes us giddy. It’s a grid of wires with ferrite toroids at every intersection. Bits can be set or cleared based on how electricity is applied to the intersecting wires. [Al Williams] walked through some of the core memory history last year and we enjoyed hearing [Pamela Liou] recount the story of how textile workers consulted on the fabrication of core memory for the Apollo missions during her OHWS Talk in October. But giddiness aside, core memory has pretty much gone the way of the dodo having been displaced by technologies that take up exponentially less space.
We chuckle at [Ken’s] mention of the core memory capacity for the IBM 1401. It has 4000 characters of memory built-in (with another 12,000 in an expansion box) and he goes on to detail that these are 6-bit characters on a machine that operates in decimal and not binary (hence 4k instead of the base-2 friendly 4096).
You may remember his work a few years back to repair core memory on the same model. The Museum has two 1401’s, which turned out to be a huge help in trouble-shooting this. After tracing out the control lines, the repair team began swapping cards between the working and non-working machines. They were able to bring it back online — establishing one of the green inductors was bad — only to be struck with a second fault in the power supply.
Get this, [Ken] comments that “the whole computer is pre-silicon”. When working through the PSU, some suspect transistors were replaced with germanium power transistors. Those may have been a red-herring, as a penciled-in fuse on the original schematics turned out to be the linchpin of the PSU repair. Buried deep in the assembly, replacing the designed-to-fail part let the ancient beast awake once more.
Machines of this quality were heavily documented, and the schematics make this type of trouble-shooting a lot more manageable. But it’s still as much an art as it is skill. Make sure to give [Ken’s] article a read, and look around at the other repair jobs he’s documented — keeping these machines in service is becoming wizard-level work and we love being able to follow along.
Next weekend is the Vintage Computer Festival West, held at the Computer History Museum. Hackaday is once again proud to sponsor this event that brings together the people and hardware that drove the information revolution. [Bil Herd] and [Joshua Vasquez] will be on hand representing the Hackaday Crew.
This year’s talks show an impressive lineup of people. [Bil Herd] will be on stage with a collection of other engineers who secured Commodore’s place in history. The Computer History Museum has a very active restoration program for original computer hardware. Friend of Hackaday, [Ken Shirriff], has been working on a restoration of the Xerox Alto and is on the panel giving a talk about the process. And just to cherry-pick one more highlight, there’s a talk on system debugging before you even turn the thing on — a topic that can save you from having a very bad day with very ancient hardware.
A great part of VCF is that the exhibits are often either hands-on or demonstrations so you can actually play around with hardware which most people have never even seen in person. Add to that the collection at the Computer History Museum plus some extra exhibits they have planned for the event and you’re likely to run out of time before you make your way through everything.
Since we’ve mentioned the Computer History Museum, we also have some upcoming news. A bit later this month, Hackaday Contributor-at-Large [Voja Antonic] has been invited to visit the museum, record his oral history, and deliver to their collection an original Galaksija computer — wildly successful first as a kit and then as a manufactured computer which he built in Yugoslavia 1983. Congratualtions [Voja]!
With almost everything that contains a shred of automation relying on a microcontroller these days, it’s likely that you will own hundreds of microprocessors beside the obvious ones in your laptop or phone. Computing devices large and small have become such a part of the fabric of our lives that we cease to see them, the devices and machines they serve just work, and we get on with our lives.
It is sometimes easy to forget then how recent an innovation they are. If you were born in the 1960s for example, computers would probably have been something spoken in terms of the Space Race or science fiction, and unless you were lucky you would have been a teenager before seeing one in front of you.
Having seen such an explosive pace of development in a relatively short time, it has taken the historians and archivists a while to catch up. General museums have been slow to embrace the field, and specialist museums of computing are still relative infants in the heritage field. Computers lend themselves to interactivity, so this is an area in which the traditional static displays that work so well for anthropological artifacts or famous paintings do not work very well.
Tucked away next to a railway line behind an industrial estate in the city of Cambridge, UK, is one of the new breed of specialist computer museum. The Centre for Computing History houses a large collection of vintage hardware, and maintains much of it in a running condition ready for visitors to experiment with.
Finding the museum is easy enough if you are prepared to trust your mapping application. It’s a reasonable walk from the centre of the city, or for those brave enough to pit themselves against Cambridge’s notorious congestion there is limited on-site parking. You find yourself winding through an industrial park past tile warehouses, car-parts shops, and a hand car wash, before an unobtrusive sign next to a railway level crossing directs you to the right down the side of a taxi company. In front of you then is the museum, in a large industrial unit.
Pay your entrance fee at the desk, Gift Aid it using their retro green screen terminal application if you are a British taxpayer, and you’re straight into the exhibits. Right in front of you surrounding the café area is something you may have heard of if you are a Hackaday reader, a relatively recent addition to the museum, the Megaprocessor.
If we hadn’t already covered it in some detail, the Megaprocessor would be enough for a long Hackaday article in its own right. It’s a 16-bit processor implemented using discrete components, around 42,300 transistors and a LOT of indicator LEDs, all arranged on small PCBs laid out in a series of large frames with clear annotations showing the different functions. There is a whopping 256 bytes of RAM, and its clock speed is measured in the KHz. It is the creation of [James Newman], and his demonstration running for visitors to try is a game of Tetris using the LED indicators on the RAM as a display.
To be able to get so up close and personal with the inner workings of a computer is something few who haven’t seen the Megaprocessor will have experienced. There are other computers with lights indicating their innermost secrets such as the Harwell Dekatron, but only the Megaprocessor has such a clear explanation and block diagram of every component alongside all those LED indicators. When it’s running a game of Tetris it’s difficult to follow what is going on, but given that it also has a single step mode it’s easy to see that this could be a very good way to learn microprocessor internals.
The first room off the café contains a display of the computers used in British education during the 1980s. There is as you might expect a classroom’s worth of Acorn BBC Micros such as you would have seen in many schools of that era, but alongside them are some rarer exhibits. The Research Machines 380Z, for example, an impressively specified Z80-based system from Oxford that might not have the fame of its beige plastic rival, but that unlike the Acorn was the product of a company that survives in the education market to this day. And an early Acorn Archimedes, a computer which though you may not find it familiar you will certainly have heard of the processor that it debuted. Clue: The “A” in “ARM” originaly stood for “Acorn”.
The rarest exhibit in this froom though concerns another BBC Micro, this time the extended Master System. Hooked up to it is an unusual mass storage peripheral that was produced in small numbers only for this specific application, a Philips LaserDisc drive. This is one of very few surviving functional Domesday Project systems, an ambitious undertaking from 1986 to mark the anniversary of the Norman Domesday Book in which the public gathered multimedia information to be released on this LaserDisc application. Because of the rarity of the hardware this huge effort swiftly became abandonware, and its data was only saved for posterity in the last decade.
The main body of the building houses the bulk of the collection. Because this is a huge industrial space, the effect is somewhat overwhelming, as though the areas are broken up by some partitions you are immediately faced with a huge variety of old computer hardware.
The largest part of the hall features the museum’s display of home computers from the 1980s and early 1990s. On show is a very impressive collection of 8-bit and 16-bit micros, including all the ones we’d heard of and even a few we hadn’t. Most of them are working, turned on, and ready to go, and in a lot of cases their programming manual is alongside ready for the visitor to sit down and try their hand at a little BASIC. There are so many that listing them would result in a huge body of text, so perhaps our best bet instead is to treat you to a slideshow (click, click).
Beyond the home micros, past the fascinating peek into the museum’s loading bay, and there are a selection of arcade cabinets and then a comprehensive array of games consoles. Everything from the earliest Pong clones to the latest high-powered machines with which you will no doubt be familiar is represented, so if you are of the console generation and the array of home computers left you unimpressed, this section should have you playing in no time.
One might be tempted so far to believe that the point of this museum is to chart computers as consumer devices and in popular culture, but as you reach the back of the hall the other face of the collection comes to the fore. Business and scientific computing is well-represented, with displays of word processors, minicomputers, workstations, and portable computing.
On a pedestal in a Perspex box all of its own is something rather special, a MITS Altair 8800, and a rare example for UK visitors of the first commercially available microcomputer. Famously its first programming language was Microsoft BASIC, this machine can claim to be that from which much of what we have today took its start.
In the corner of the building is a small room set up as an office of the 1970s, a sea of wood-effect Formica with a black-and-white TV playing period BBC news reports. They encourage you to investigate the desks as well as the wordprocessor, telephone, acoustic coupler, answering machine and other period items.
The museum has a small display of minicomputers, with plenty of blinkenlight panels to investigate even if they’re not blinking. On the day of our visit one of them had an engineer deep in its internals working on it, so while none of them were running it seems that they are not just static exhibits.
Finally, at various points around the museum were cabinets with collections of related items. Calculators, Clive Sinclair’s miniature televisions, or the evolution of the mobile phone. It is these subsidiary displays that add the cherry to the cake in a museum like this one, for they are much more ephemeral than many of the computers.
This is one of those museums with so many fascinating exhibits that it is difficult to convey the breadth of its collection in the space afforded by a Hackaday article.
There is an inevitable comparison to be made between this museum and the National Museum of Computing at Bletchley Park that we reviewed last year. It’s probably best to say that the two museums each have their own flavours, while Bletchley has more early machines such as WITCH or their Colossus replica as well as minis and mainframes, the Centre for Computing History has many more microcomputers as well as by our judgement more computers in a running and usable condition. We would never suggest a one-or-the-other decision, instead visit both. You won’t regret it.
The Centre for Computing History can be found at Rene Court, Coldhams Road, Cambridge, CB1 3EW. They are open five days a week from Wednesday through to Sunday, and seven days a week during school holidays. They open their doors at 10 am and close at 5 pm, with last admissions at 4 pm. Entry is £8 for grown-ups, and £6 for under-16s. Under-5s are free. If you do visit and you are a UK tax payer, please take a moment to do the gift aid thing, they are after all a charity.
Here’s a question for you all: how will you know when you are no longer young? When you fall out of love with contemporary popular music perhaps, or start to find the idea of a cruise holiday attractive? The surefire sign for many people is having to ask a teenager how a piece of technology works — this is probably not that applicable to most Hackaday readers.
How about when you’re shocked to encounter a significant part of your youth in a museum? These are supposed to be places of The Olden Days, full of rustic agricultural tools or Neolithic pottery, yet here you are in front of your teenage years presented for all to see. You have two choices: you can surrender to the inevitable and henceforth only wear beige clothing, take up golf or maybe book that old person’s cruise holiday, or you can dive in misty-eyed and reacquaint yourself with everything in front of you.
The above is probably an experience many regulars of these pages would share on a visit to Britain’s National Museum Of Computing in a corner of the famous Bletchley Park site, home of Britain’s wartime codebreaking efforts. They describe what they do on their web site as follows:
“We conserve, restore, reconstruct, and give hands-on access to historic computers and related artefacts – with a particular focus on those which were the result of pioneering British ingenuity.“
For the visitor this means that their galleries contain a huge array of computing and associated equipment, many of which are presented as working exhibits without too much of the dumbing-down that pervades so many other museums, and that the staff are extremely knowledgable about them.
The museum is housed in one of the groups of wartime codebreakers’ huts, laid out roughly in the shape of a capital H with the top of one vertical lopped off. If you are a connoisseur of British wartime sites you’ll recognise these buildings, they were built to a fairly standard design all over the country. Internally this means that the galleries are structured around the long corridors that are a staple of that era, giving in particular the earlier exhibits a feel of their time.
Old mainframe computers are interesting, especially to those of us who weren’t around to see them in action. We sit with old-timers and listen to their stories of the good ol’ days. They tell us about loading paper tape or giving instructions one at a time with toggle switches and LED output indicators. We hang on every word because its interesting to know how we got to this point in the tech-timeline and we appreciate the patience and insanity it must have taken to soldier on through the “good ol’ days”.
Ken describes in thorough detail how the IBM 1401 — which was first introduced in 1959 — takes a decimal number as an input and operates on it one BCD digit at a time. Before performing the instruction the BCD number is converted to qui-binary. Qui-binary is represented by 7 bits, 5 qui bits and 2 binary bits: 0000000. The qui portion represents the largest even number contained in the BCD value and the binary portion represents a 1 if the BCD value is odd or a 0 for even. For example if the BCD number is 9 then the Q8 bit and the B1 bit are set resulting in: 1000010.
The qui-binary representation makes for easy error checking since only one qui bit should be set and only one binary bit should be set. [Ken] goes on to explain more complex arithmetic and circuitry within the IBM 1401 in his post.
If you find yourself in the vicinity of Mountain View, California you really should stop by the Computer History Museum. Even if you aren’t into the retrocomputer scene, there’s so much cool hardware ranging from a replica of the Babbage engine to nearly modern PCs. There’s even a room dedicated to classic video games. There are two fully working old computers at the museum that have their own special rooms: a PDP-1 (complete with vector scope to run Space War) and an IBM 1401.
The IBM 1401 looks like big iron, but in its day it was a low-end machine (costing an innovative business about $2500 a month). The base unit had 4000 words of magnetic core memory, but if you had a hankering for more memory, you could add the 350 pound dishwasher-sized IBM 1406 (for only $1575 a month or you could buy for $55100). How much memory did you get for $18900 a year? An extra 12000 words!
The problem is, the museum’s 1406 had developed a problem. Some addresses ending in 2, 4 or 6 failed and they were all in the same 4K block. [Ken Shirriff] was asked to go in and try to find the problem. We don’t want to give away the story, but [Ken] wrote up his experience (with lots of pictures).