Reply to post: Re: you can't write a pre-emptively multi-tasking OS for the 8086

Rust in peace: Memory bugs in C and C++ code cause security issues so Microsoft is considering alternatives once again

bombastic bob Silver badge
Meh

Re: you can't write a pre-emptively multi-tasking OS for the 8086

actually you can write a pre-emptively multi-tasking OS for just about ANY processor, but in some cases (68k was one of them) you had to jump through some odd hoops to make your program relocatable to any block of memory [which is really what you need to happen if you don't have virtual memory management].

The old PDP-11's had the ability to have multiple users, in some cases without memory management hardware [which would virtualize your memory space]. One particular package 'MU Basic' (MU stood for Multi User) managed that well enough, maybe 4 simultaneous users running BASIC on a system with only 32k words (64k bytes) of RAM on it. You didn't get much for each user, but it worked, it was mutli-user, pre-emptive, etc..

Not as good as 286 or later Intel CPU with the built-in virtualized memory capability (selectors vs segments, for example, which make memory relocatable, and also 386+ with page tables) but it COULD be done. And 68k's had to use "pseudo segments" that were used by Apple's OS for quite a while, as I understand it to make their code relocatable. Similarly on the Palm devices (which used a 68k) you had something similar to that.

Anyway... just sayin', you CAN write a pre-emptively multi-tasking OS for the 8086. I just wouldn't WANT to.

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