Xref: utzoo comp.sys.mac.misc:13088 comp.windows.ms:13751
Newsgroups: comp.sys.mac.misc,comp.windows.ms
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From: tom@mims-iris.waterloo.edu (Tom Haapanen)
Subject: Re: Mac Vs. Windows? (sorry)
Message-ID: <1991Jun12.224847.4262@watserv1.waterloo.edu>
Sender: news@watserv1.waterloo.edu
Organization: University of Waterloo, WATMIMS Research Group
References: <0E010021.e0mxxc@gla-aux.uucp> <1991Jun4.154854.19649@dbase.A-T.COM> <56nD02AQ08cd01@JUTS.ccc.amdahl.com> <1991Jun12.055711.21457@cs.yale.edu> <1991Jun12.152813.20074@leland.Stanford.EDU> <1991Jun12.154934.20965@aero.org>
Date: Wed, 12 Jun 1991 22:48:47 GMT
Lines: 32

John Doner <doner@Aero.org> writes:
> aaron@jessica.stanford.edu (Aaron Wallace) writes: 
>|> I've never actually programmed a Mac [...]  I remember
>|> having to worry about arranging static data into segments and getting
>|> segment too large errors.  I've read elsewhere that, lovely as the linear
>|> address space is, Apple went through all kinds of hoops and backflips to
>|> simulate a segmented memory system on the Mac.

> What looks like a segmented memory system to some is mainly just a compiler
> limitation.  They use 16-bit integers as array subscripts, so arrays get 
> limited to 2^16.  They always generate branches using the 16-bit offset 
> instructions, instead of the 32-bit ones, so CODE segments get limited to
> 32K.  None of this is Apple's doing, or intrinsic to the hardware or the
> Mac OS.

Having done development work on a Mac since early January, 1984 (although
admittedly not recently), I can confirm that it is *NOT* a MC68000 or Mac
hardware limitation.  It is, however, a limitation built into the Mac OS,
designed to make it possible to run reasonable apps on a machine with just
128K or RAM.  by swapping segments in and out of main memory. That, of
course, is just like Windows' segment-swapping.

> Actually, it's hard to fault the compiler writers.  It seemed so reasonable at
> the time.  But with today's cheap memory, it's a bad idea to build those 
> limitations into the compilers.

Compiler writers?  Heck, we were using a cross-assembler to do this, and we
had the same limitation!  There weren't a lot of development tools available
before January 24...

[ \tom haapanen --- university of waterloo --- tom@mims-iris.waterloo.edu ]
[ "i don't even know what street canada is on"               -- al capone ]