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From: pickle@nmtvax.UUCP
Newsgroups: net.micro.amiga
Subject: MMUs and program correctness
Message-ID: <862@nmtvax.UUCP>
Date: Sun, 10-Nov-85 23:11:57 EST
Article-I.D.: nmtvax.862
Posted: Sun Nov 10 23:11:57 1985
Date-Received: Thu, 14-Nov-85 02:55:50 EST
Distribution: net
Organization: New Mexico Tech, Socorro
Lines: 35

neil@amiga.UUCP from Commodore-Amiga Inc. writes:
>Multitasking does NOT require an MMU.  Processes are allocated separate
>places in memory, and then are timesliced (the same way one would if one
>did have an mmu...).  There is no protection between different processes.
>One could write a program that trashes memory, and therefore the system
>(hence the infamous "GURU MEDITATION...").
>Correctly written programs run without any problems, however.

    Whoa!!  The way *I* would phrase it is "Multitasking does not require
an MMU, but it's a good idea to have one."  A few questions on this: does
the OS take care of memory allocation while a program is running, or
only when loading?  For example, I write a quick sort in C that I want
to keep around in background.  Every once in a while, I feed it source
and destination files, the program mallocs a bunch of space, sorts,
writes, then frees the space.  When I call malloc, does the OS handle
it, or does the C compiler put in code to grab whatever looks good?
If the actual code is ~5k, and I read in 50k of data, will this cause
a problem?
    From a development point of view, this scheme is really bad: nothing
would frost my cookies more than having to reboot the system because
I looked at a bad pointer and a program I was writing decided to munch
some chunk of memory.  What makes it worse than other micros?  Imagine
that I store variable x in the middle of my editor.  The program stops,
I go to edit the program, and the machine takes a holiday.  Multitasking
while developing might not be a good idea....
    Of course none of this happens because we all write programs correctly,
right? %\' (Impressionist smile)
    On a lighter note, I recall reading that the Joyboard (a joystick
you stand on) was being used to generate capital for a high powered
graphics/sound computer.  The Amiga wouldn't happen to have any relation
to this, would it?

Patrick "Pickle" Madden, in Scenic Socorro (It's worth the stop)
!cmcl2!lanl!unmc!nmtvax!pickle  "You needn't be well to be wealthy,
!ucbvax!unmvax!nmtvax!pickle     But you've got to be whole to be holy"