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From: Brett <ggtgp@yahoo.com>
Newsgroups: comp.arch
Subject: Re: What is an N-bit machine?
Date: Sat, 30 Nov 2024 01:29:04 -0000 (UTC)
Organization: A noiseless patient Spider
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Lawrence D'Oliveiro <ldo@nz.invalid> wrote:
> On Thu, 28 Nov 2024 22:08 +0000 (GMT Standard Time), John Dallman wrote:
> 
>> In article <viao3r$na9e$4@dont-email.me>, ldo@nz.invalid (Lawrence
>> D'Oliveiro) wrote:
>> 
>>> Apple went through the same sort of thing. Yet it managed the 
>>> transition much more cleanly.
>> 
>> Apple simply demanded all software become 32-bit clean. The fact that
>> they didn't forsee the problem and warn software writers not to use the
>> high 8 bits rather implies they weren't paying attention. 
> 
> Oh, they were paying attention, all right. In the original 1984 Macintosh 
> software, the top 8 bits in a “handle” (pointer to a pointer to a 
> relocatable block) were used to store handle state (e.g. whether the block 
> was locked in a particular memory location). But there were no API calls 
> to save/restore this state. That was fixed in the Mac Plus in 1986. So all 
> had to happen was for app developers to use the new calls, instead of 
> peeking at bits directly.

Yes Apple mostly hid their private use of the high byte, so software would
not break when they upgraded.

There was one obsolete API call that had a warning that it was only 24 bit
safe, and my favorite game Civ IV used that call instead of the modern
replacement.

I know this because I jumped into the debugger to see why it crashed.

>>> This in spite of having an installed base that was orders of 
>>> magnitude larger than the IBM System/360 family.
>> 
>> Apples and oranges. IBM had fewer but much larger customer
>> organisations, and could not afford to upset them much.
> 
> IBM had legendary market power, all the way up to monopoly status. 
> Whatever it decreed, its market had to follow.
>