Re: "Real" Multitasking (Re: GNO questions...)

[vandry@CAM.ORG (Phillip Vandry)]

gt2011a@prism.gatech.EDU (gt2011a SIMMS,WILLIAM SHELDON) writes:

>Huh?! I do this all the time on a Mac II running system 7. I use zmodem to
>download Apple II and Mac files while doing something else (usually a game)
>in the foreground. I have downloaded files size > 500k in the background
>without error while playing arcade-style games in the foreground to pass the
>time. The only time the zmodem download even pauses is during disk access,
>and then it picks right up when the processor is returned. I suppose an
>XOFF/XON sequence occured, but it works fine.

Many MAc implementations of ZMoem use interrupts to insure that they will
have control at given intervas. I know this is the case for MacIntercom, and
probably others as well.

This, again, is an example of having to make your own routines (the
interrupt handler, the code that installs it, etc...) becase the
cooperative system simply won't do it for you.

Notice that these programs use interrupts to gain control no matter
what. The word "Preemptive multitasking" comes to mind. OF course it's
not really preemptive multitasking, only a partial attempt at something
similar to it.

You don't see progrms for preemptive multitaskers implementing
cooperatie multitasking because it has advantages in soe situations.
That's because it doesn't.
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| Phillip Vandry | Vandry@Cam.Org | Suicide (n.): What to do if Macs   |
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