The result is a $4 Z80 home computer, and a great Hackaday Prize entry to boot. So, what do he need to build a retrocomputer loaded up with Forth, CP/M, and Basic? A CPU is a necessity ...

Back in the 1980s however, you generally had little choice: a certain home computer came with a certain OS, and that was it. If yours was based on a Z80 processor, chances are it ran CP/M.