Historical question: Longevity of Colossus.

[Quentin Campbell]

On Mon, 2 Aug 1999, Paul Leyland wrote:

> My question: why did GCHQ keep *two* of them for so long?  If they only had
> one, it could have been an exhibit in a museum.   Keeping two bits of kit,
> each occupying several cubic meters and requiring 5.5kW of power to run
> suggests that they were still useful.
> 
> Does the answer to this question have any relation to the observation that
> the design of Colossus was classified until very recently?
> 
> 
> Paul

Brian Randell is probably among the best placed on this list to help
answer that.

A couple of things I recall from talks given here:

1. At the end of the War, Donald Michie and others tried "programming"
   a Colossus to do some non-cryptographic computations. I also understand
   it was tried on some cryptographic tasks for which it was not
   originally designed. It may be it had some utility in these other areas
   that extended its useful life.

2. Tony Sale has also said that there are some analysis algorithms that
   are built into the logic of Colossus and which could be selected as
   part of its set-up menu that remain classified still. He was told
   that some of these techniques were still in use at Cheltenham until
   fairly recently.
 
Quentin
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