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From: usotsuki at buric.co (Steve Nickolas)
Subject: [TUHS] Apple IIe Unix?
Date: Fri, 27 Nov 2020 07:20:38 -0500 (EST)	[thread overview]
Message-ID: <alpine.DEB.2.21.2011270713470.14072@sd-119843.dedibox.fr> (raw)
In-Reply-To: <20201127115444.E581018C091@mercury.lcs.mit.edu>

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.

-uso.


  reply	other threads:[~2020-11-27 12:20 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-27 11:54 jnc
2020-11-27 12:20 ` usotsuki [this message]
2020-11-27 16:22 ` cowan
2020-11-28 23:12 ` dave
     [not found] <20201201160105.1359e68b.ref@algol>
2020-12-01 15:01 ` Jose R. Valverde via TUHS
2020-12-01 15:48   ` Will Senn
  -- strict thread matches above, loose matches on Subject: below --
2020-11-26 21:55 will.senn
2020-11-26 22:22 ` usotsuki
2020-11-26 22:30 ` nikke.karlsson
2020-11-27  0:24   ` drsalists
2020-11-26 22:47 ` dave
2020-11-26 23:07   ` katolaz
2020-11-26 23:00 ` clemc
2020-11-27  0:47   ` athornton
2020-11-27  3:16   ` usotsuki
2020-11-26 23:22 ` jason-tuhs
2020-11-27  3:18   ` usotsuki
2020-12-03 18:40 ` Chris Hanson

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