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If you weren't busy in the 80s trying to get the maximum of gaming power out of your C64, Amiga 500 or ATARI ST, then there is at least a probability greater than 0 that you a) are already a bit older and b) surely didn't get past CP/M.

Do you want to refresh your knowledge or even start from scratch?

Herbert R. Johnson has compiled a more than useful compendium with How to start with CP/M. Black letters on a white background, but who could afford a color monitor back in the 80s? 😁