[t43562]

Appended is a walkaround video of the Colossus at the National Museum of Computing next to Bletchley Park which is, FYI, a much better and far more interesting place to visit than Bletchley Park itself on the same site - and much cheaper. They have a bombe that cracked enigma, the colossus and some other German encoding machines and they are incredible to see. The lectures were absolutely fascinating.

https://www.youtube.com/shorts/W7w6YXaNvt8

[RugnirViking]

I used to work there. I highly recommend the harwell dekatron or WITCH. It's another very old computer, 1950s. newer than colossus, but much easier to understand. It has decimal memory banks that light up, so you can literally see the memory, each of the registers, etc. If you go at the right time or ask a staff member very nicely you can see the debug mode where it can step instruction by instruction, and operation by operation through the machine code, and see the memory change at each step.

I also recommend if you have any mathematical chops asking staff about the process of cryptanalysis on enigma, and if you're really hardcore, lorenz. Its fascinating and if you get the right staff, they really have the knowledge to take you deep into how it was done. Yes many know about the exploit of using date/weather strings that appeared in a standard form, but exactly how that was used together with a huge amount of encrypted message data to reverse engineer the functioning of the machine they hadn't seen for lorenz is bonkers.