Perhaps you're using some idiosyncratic definition of "preemptive" and "multitasking", but to me that statement's not accurate. Let's take the "multitasking" part first: that just means 'two or more computations can run at the same time, sharing the machine' - and that's not hard to do, without special hardware, provided there's some way (in the organization of the software) to save the state of one when the other is running. Many simple systems do this; e.g. the MOS system that I used on LSI-11's, BITD. "Preemptive" is a bit trickier, because things have to be organized so that one 'task' can be temporarily stopped arbitrarily (i.e. without it explicitly giving up the processor, which is what e.g.MOS did) to let another run. There does need to be some asynchronous way of inciting the second 'task' to run, but interrupts (either clock, or device) do that, and pretty much every machine has those. MINI-UNIX, for example, has premptive multitasking. The thing that takes special hardware is _protecting_ one task from a bug in another - a bug which could trash the first tasks's (or the system's!) memory. One has to have memory management of some kind to do that. MINI-UNIX would be a good place to start if one wanted to bring up a system on a machine without memory management; there's nothing in the kernel which is PDP-11 dependent that I can think of (unlike V6, which had a fairly heavy dependency on the PDP-11 memory management hardware - although one could of course rip that all out, as MINI-UNIX did). However, one's still looking at a fair amount of work, both to get rid of any traces of PDP-11isms (e.g. stack growth direction), and translate the assembler part (startup, and access to non-C operations). Something like FUZIX might be an easier option. Noel