OK Mac-heads:

What actually changed between Mac OS 9.0.4 to 9.1 re: memory management?

Emaculation forums and other sources frequently mention that SheepShaver can't run 9.1 and up because of lack of emulating an MMU.

But Apple's own system requirements for 9.1 say it could run on any PowerPC machine:

Am I correct assuming all PowerPC Macs had MMUs then? So if it like wasn't an actual hardware change, what happened here?

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@The_BFOOL has to do with a requirement in 9.1 and 9.2 for MMU. 9.2 was only released to run in classic mode through OSX PowerPC processors. So 9.0 is sufficient for emulation.

@The_BFOOL I don’t think sheepshaver was ever built to support MMU.

@Thorsted right, to clarify it's not really a matter of "needing" 9.1 or 9.2 (and QEMU *does* emulate MMU anyway if you really did need it) - always just a nagging curiosity/trying to understand under-the-hood!

@Thorsted I guess my scenarios/source of confusion are:

- if all real-world PowerPC Macs had MMUs, why wait until 9.1 to *require* them in the system code
- if not all real-world PowerPC Macs had MMUs, why wouldn't that come up as a system requirement for 9.1?

@Thorsted asked and got a terrific answer from the Emaculation forum!

the shift was that 9.1 finally relied on/required the Carbon API to boot (in anticipation of transition to OSX and that 9.1 would be largely used for the Classic Environment, as you said), and Carbon needs MMU. SheepShaver skates by b/c they just never *relied* on MMU to run the OS on most PPC models even tho they all had one

@Thorsted interesting comparison from that user to how recent macOS Intel versions can still run/boot in QEMU even though QEMU can't properly emulate any Apple GPU

@The_BFOOL Makes sense. I remember when they switched from Motorola to Intel and being frustrated, as I alway have a need to run old stuff. Apple isn’t making it easier, but at least the vintage/gaming community is!

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