These mostly 8-bit processors were the power behind Legacy Computers.
MOS 6502
Building a transistor-scale 6502
COSMAC 1802
The COSMAC 1802 processor was 8-bit external, with 16x16-bit internal registers, a clean instruction set, and was clockable right down to DC (which is why it was a popular choice in space probes).
All done with 5,000 transistors, in 1976. Astonishing.
GOFAI, FORTH, and the 1802 processor illustrate what tight constraints can sometimes lead to. It’s an important lesson that sometimes gets lost in the modern world of vast computational resources.