Even DRI's MP/M from 1979 had preemptive multi-tasking, as long as the platform supported an clock interrupt. You can find the documents on bitsavers, the bina

Even DRI's MP/M from 1979 had preemptive multi-tasking, as long as the platform supported an clock interrupt. You can find the documents on bitsavers, the binaries may well be there and/or on Gaby's site.