computer history museum

10 Articles

Review: The National Museum Of Computing

September 13, 2016 by 32 Comments

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.

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The IBM 1401’s Unique Qui-Binary Arithmetic

November 5, 2015 by 12 Comments

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 Shirriff] is making those good ol’ days come alive with a series of articles relating to his work with hardware at the Computer History Museum. His latest installment is an article describing the strange implementation of the IBM 1401’s qui-binary arithmetic. Full disclosure: It has not been confirmed that [Ken] is an “old-timer” however his article doesn’t help the argument that he isn’t.

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 aren’t familiar with [Ken], we covered his reverse engineering of the Sinclair Scientific Calculator, his explanation of the TL431, and of course the core memory repair that is part of his Computer History Museum work.

Thanks for the tip [bobomb].

Repairing $55,000 Of Vintage Core Memory

October 19, 2015 by 16 Comments

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).

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