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From: ph@cci632.UUCP (Pete Hoch)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Why do application partitions exist?
Summary: Long ago and far away.
Message-ID: <50284@cci632.UUCP>
Date: 6 Feb 91 15:34:04 GMT
References: <1991Feb5.182501.4325@wam.umd.edu>
Organization: Computer Consoles Inc. an STC Company, Rochester, NY
Lines: 23

nebel@wam.umd.edu (Chris D. Nebel) writes:
> I got to wondering about this one late one night: why does Multifinder have
> this business of application partitions?  Why couldn't it have been written
> so that all applications simply share one big heap zone?  This would have
> a number of advantages: users don't have to know anything about partition
> sizes, you don't have wasted memory because of apps only using small portions
> of their partition, having enough contiguous free memory to run a program
> becomes much less of a problem, and programmers don't have to worry about
> special Multifinder temporary memory.

It seems to me you are asking, 'Why didn't Apple impliment a demand
paging system in Multifinder?'.  Or at least something like that.

As I understand it, the first reason is that applications cannot run
in supervisor mode when you do this.  Now Apple has been saying for
years, "Do not run is suppervisor mode.".  But I don't think you
actualy break now if you do it.  Next you need protected memory to
do this.  Since this is not planned for system 7.0 I would not expect
paging to be implimented soon.  The last thing that I can think of
is I imagine many programs assume a contiguous memory space.  This
obviously would not be the case in sharing one application heap.

Pete