[TUHS] Apple IIe Unix?

Steve Nickolas usotsuki at buric.co
Fri Nov 27 22:20:38 AEST 2020

On Fri, 27 Nov 2020, Noel Chiappa wrote:

>    > From: Steve Nickolas
>    > there's no easy way to do preemptive multitasking without extra
>    > hardware.
> 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.

That's cooperative multitasking, though.  And there's actually a program 
for the Apple //e that lets you do it from *BASIC*, "Extra.Apple" from 
Beagle Bros (they did a ton of "enhancement" utilities like this).

> "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.

You'd at least need interrupts, but a stock Apple //e literally doesn't 
have any way to generate a hardware interrupt.

I do believe the //c (which has a built-in mouse controller which is 
interrupt-driven) can be programmed to do that, but without something like 
a 6522 card, a //e can't.  It's pretty primordial, really.


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