If you’ve visited the Centre For Computing History recently, you will have had a chance to see James Newman’s Megaprocessor, and perhaps to see the man himself explaining it. But even if not, you can learn a lot from his website and videos:
The Megaprocessor is a 16 bit processor. There are four general purpose 16 bit registers: R0, R1, R2, R3. There is a program counter, PC. A register dedicated as the stack pointer SP. And a processor status register, PS. For computation there is a 16 bit ALU and a 16 bit adder.
From the vital statistics page, we learn it’s made with tens of thousands of transistors and ten thousand LEDs, weighs half a ton and uses only 500W to run at about 20kHz. (“an 8-bit adder is about a foot long”)
See also these playlists for more on how the machine works and how it was built: