Oldest operational computer was Re: cctalk Digest, Vol 54, Issue

I think you need to be more specific. The laws of physics and chemistry have, AFAIK, not changed since 1900. The necessary raw materials to make transsitors and ICs were around then. So from what you said, you could just use a microprocessor.... So I think you have to consider just what you are, and are not, allowing with respect to making devices to make components, etc. Relays were certainly well known and understood at that time. I would propose a relay logic machine, therefore. Unfortunately my books on telegraphy are about 10-15 years too late. Some of the stuff in there could well be very applicable if it was known at the time you want. For example, and going a bit off the thread, one of my old books on electrical engineering describes a system used on the London Underground (underground railway, subway, call it what you will) to keep track of the trains. Each train had a 4 bit code, there was a drunm with 4 rows of pins whcih could be moved itn oone of 2 states to stoe the IDs of the trains. A set of solenoids moved the pins, the drum was then stepped to the next positon. A separate rotating set of contacts read out the states of a a row of pins and then moved on to the next one. It worked just like the classic circular queue with seaprate read and write pointers that we've all implemented in software at some point. The outputs of the contacts were decoded by a 'tree stucture' of relays to produce a 1-of-16 output. Now, as I said, I don;t know if that was around in 1900, but it certainly _could_ have been, The electric light bulb was known before 1900. The Edison Effect (diode valve) was, IIRC 1883. THe triode, was, alas, later (1907 I think), but maybe you'll stretch the point and allow it. -tony