[rescue] FTGH: Macintosh LC475

[Liam Proven]

On Tue, 12 Oct 2021 at 17:08, Jonathan Patschke <jp at celestrion.net> wrote:
>
> It's pretty annoying that way, and seems like the silliest sort of
> oversight, given that 32-bit-clean Macs were the obvious way forward
> when the card came out.

I guess so, but to be fair, the IIe option board did come out 3Y
before the LC475 and 7Y before MacOS 7.6...

https://en.wikipedia.org/wiki/Apple_IIe_Card

And given that it does some fairly low-level jiggery-pokery to map Mac
peripherals into the emulated Apple ][ I am not very surprised that
it's not all that compatible. I remember the days of MODE32 and so
on...

https://en.wikipedia.org/wiki/MODE32

Quite a few things broke.

Interestingly, Acorn RISC OS had similar problems. Up to v4, RISC OS
used the ARM's 26-bit mode, and some flags were kept in the upper bits
of each byte, broadly similarly to how older versions of MacOS did it.

RISC OS used an ARM mode called 26-bit mode

https://www.riscos.info/index.php/32bit

https://en.wikipedia.org/wiki/Classic_Mac_OS_memory_management#32-bit_clean

But by the time of ARM devices such as the XScale, which mainly ran
xNix derivatives or Symbian and so on, ARM removed 26-bit mode,
stranding RISC OS. The company that bought the official licence to
continue Acorn's unfinished RISC OS 4 had continued to market 26-bit
upgrades. It didn't know that Pace, a set-top box and NC maker, _also_
had a licence. Pace had ported RISC OS to 32-bit clean ARMs, and this
enabled another company, Castle Technologies, to licence the 32-bit
clean RISC OS, call it RISC OS 5 and offer a new faster RISC OS
machine, the Iyonix, with a 32-bit bit OS on a 32-bit ARM chip.

So the OS didn't die but this resulted in 2 forks: the
all-closed-source RISC OS 4 from RISC OS Ltd, which was mainly aimed
at older 26-bit machines, and the newer, shared-source and later FOSS
32-bit RISC OS 5, which now runs on things like the Raspberry Pi and
PineBook.

So, all in all, I reckon Apple handled the 24-bit to 32-bit addressing
move more gracefully than the RISC OS world did. :-) Most apps still
worked, just some older machines had problems with new OS releases,
some of which could be patched to work, and some old hardware got left
behind.

Of course Apple made an _awful_ lot more money and could afford more R&D. ;-)

-- 
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