On Tue, 20 Nov 2012 15:21:02 +0000, Tim Watts wrote:
I thought they had an even older "Colossus" up and running? I saw the
"Bombe" running at Bletchley that predated even that.

The designs did but both were IIRC rebuilt from scratch.

WITCH is unique in that is was stored as an original kit of modules from
the original machine and apparantly most of the dekatrons still worked.

The critical thing is that Colossus isn't a stored-program machine (which
upsets some of the purists who therefore don't class it a a computer),
whereas Witch is.

The rebuild nature of Colossus doesn't seem to generally bother people
IME - it's seen as a faithful-enough system that it's the best that can
be done under the circumstances (there might be a chance that GCHQ have
one or two originals in one of those warehouses like at the end of
Indiana Jones, but after so long it's probably unlikely

I did take the trouble to ask, and the majority of Colossus is fabricated
from GPO parts that are identical to what the originals used - although
they came out of phone exchanges which were much later. There are some
modern resisors and capacitors in there, and the wiring is all modern
PVC; the originals would have had cotton-covered enamelled wire, but
apparently that stuff isn't particularly pleasant (particularly when
hauled out of rat-infested old exchanges :-)

cheers

Jules