I share an interest in old computing technology with several of my friends and readers. An interesting sub-topic within this vast area is the world of computers based upon relays. In the last couple of days, I found cool links to two different relay based computing projects, so I thought I'd pass them along.
First is Jon Stanley's Relay Computer Two. Consisting of 281 relays, it boasts an 8 bit data bus and a 16 bit address bus. His website gives the kind of dense, technical information that I like to see from a project like this. You'll see how he implements adders (using Konrad Zuse's design which constructs a one bit full adder out of two 4PDT relays). Very neat. Lots of cool details. It clanks along at less than 30 cycles per second. Yes, it uses solid state memory (as almost all amateur reconstructions do, it's simply to expensive to do otherwise) but the result in a clicky, clanky marvel. Check it out (and make special note of the enormous capacitor in the power supply):
Then there is Rory's awesome series of relay based computers, culminating in the TIM-8. There are all sorts of awesome laudable features in this build. He didn't want to "cheat" and use solid state memory, so he struggled to find solutions. He ends up storing programs on paper receipt tape as a series of black and white lines which provide control signals to the rest of the computer. These are then loaded onto a motor driven spindle and read by a series of phototransistors (I think, not clear). The tape is rewound and replayed during program execution. Very cool. He also constructed his own solid state memory out of capacitors, with a density of about 9 bits per cubic inch. Very, very cool. Here's one of his videos, but search around on his site, he has more: