I’m kind of on a retro computing kick for the last few weeks. I suppose it is mostly because I picked up an FPGA board to experiment with, and I have been reading old books on computer architectures, looking for old fun machines that were simple enough to implement in VHDL/Verilog. This brought me back to the Apollo Guidance Computer which was implemented using mostly 3 input NOR gates implemented as ICs and RTL (not TTL) logic.

So, I looked up what that those look like. And they are actually pretty simple: a simple RTL inverter is just a transistor and two resistors. A NOR gate isn’t much worse. So, I thought about building some HSI “chips” using some breadboards, pins on a 0.2″ spacing, some cheap transistors and resistors. The question is what is the most complex circuit I could actually do with this technique?