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From: torrie@cs.stanford.edu (Evan Torrie)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: 8-bit death (was Re: What the heck IS "Interactive TV"?)
Message-ID: <1991Apr22.175525.2785@neon.Stanford.EDU>
Date: 22 Apr 91 17:55:25 GMT
References: <10944@mentor.cc.purdue.edu> <1991Apr21.195406.25574@sugar.hackercorp.com> <1991Apr22.021234.23673@neon.Stanford.EDU> <1991Apr22.101854.3301@sugar.hackercorp.com>
Sender: torrie@neon.Stanford.EDU (Evan James Torrie)
Organization: Computer Science Department, Stanford University, Ca , USA
Lines: 46

peter@sugar.hackercorp.com (Peter da Silva) writes:

>In article <1991Apr22.021234.23673@neon.Stanford.EDU> torrie@cs.stanford.edu (Evan Torrie) writes:
>>   The only address space limitation in the original Mac OS was a 24-bit limit
>> on pointers (and hence program addresses), since the upper 8 bits of a pointer
>> address were used for memory management. [This is now fixed in System 7.0, 
>> following on from A/UX which fixed it 2-3 years ago].

>Well, there was also the 128K available memory limit, 

  Yes, but this was a hardware limit, not an OS limit.  There were no
changes necessary to the OS when the memory went to 512K and then 4MB.

>Plus, didn't a whole
>bunch of stuff stop working when you went over 1M... and that's only 20 bits.

  As far as I know, Microsoft Excel 1.0 was the only program which
exhibited this behaviour (if you put it above the first 1MB of
memory).  This was somehow related to Microsoft's peculiar,
non-standard PCODE system at the time.  Other vendors programs weren't
so affected (admittedly, Microsoft had some reason to do this - it
allowed them to run Excel in 512K of memory while similar spreadsheets
required 1MB).

>Anyway, the amount of memory available for the O/S in the original Mac was
>pretty much the same as it was for 8-bit "operating systems" like
>CP/M. 

  Yes, but the OS was not an 8-bit OS - only the particular
implementation of the hardware at that time.

>Thus
>you had a single-tasking, flat file system (when PRO Dos, on the Apple ///,
>already had directories), and so on.

  Yes, both of these were bad decisions, given that they'd already had
experience with both of these in the Lisa.  The flat file system was
particularly poor.  Luckily, they managed to graft HFS on top
reasonably successfully (and HFS continues to be one of the better file
systems around).  They weren't so lucky with multitasking. 

-- 
------------------------------------------------------------------------------
Evan Torrie.  Stanford University, Class of 199?       torrie@cs.stanford.edu   
"Dear Fascist Bully Boy,   Give me some money, or else.  Neil.  P.S. May
the seed of your loins be fruitful in the womb of your woman..."