Without a memory mapper or scheduler it's hard to write a multitasking OS.

detaro · on Oct 13, 2021

Not in the sense we usually mean nowadays, but assigning pages to processes and switching between them, with a small non-paged segment for general data/code lets you build multitasking systems. E.g. I believe early multiuser BBSes ran on systems like that.

vidarh · on Oct 13, 2021

There were tools that added multitasking to the C64, such as e.g. BASIC Lightning that let you run multiple BASIC "threads" + sprite animations at the same time.

It's easy to write a scheduler for a 6502 as there's so little to save, though you'll need to be very careful about stack usage, and you might do better with a specialised scheduler (e.g. for C64 BASIC) as a lot of code you might want to run may store additional state in fixed locations.