I was about to write CP/M is at least essential for enjoying The Hitchhiker's Guide to the Galaxy as Infocom text adventure (like I did on the Atari ST with CP/

I was about to write CP/M is at least essential for enjoying The Hitchhiker's Guide to the Galaxy as Infocom text adventure (like I did on the Atari ST with CP/M emulator), but then I learnt it was available on most other OSes at the time as well, including on Atari/TOS native.