8-bitters and multi-whatever

CP/M or most other OSs for non 8080/z80 could easily be fooled into redirecting disk IO to a serial port. Though CP/M was modular enough and most widespread it was most often hacked that way. There is however no rule that says a OS must talk to a disk as storage and once that is clear then it's easy to cobble up a packet protocal that transmits the needed data across a serial or parallel port to a willing and enabled host. Some systems like the big S100 crates or multibus running MPM used the bus and some common memory so that multiple CPUs typically z80 with 128k ram, rom and serial IO plus a bus interface and memory manangement for off board memeory. MPM would be the server and CP/M would be the local cpus that users interacted with. It wasn't seen often as it was expensive to ahve the hardware and the average hobbiest at the time rarely had more than one fully functional system and maybe a SBC of the KIM-1, EVK68, AIM65 or SDK85 level.