4 ms·

Didn't last Mac OS 9 versions have memory protection? I mean there's a reason it's hard to run 9.2 on an emulator — it requires a working MMU.

tambourine_man 5y ago
No, after 8.6 the system featured a micro kernel on which the old OS ran atop. I think you could opt in for better stability, but I'm not sure. But most of the OS and apps still ran on the same shared memory space with cooperative multitasking, meaning a single app could (and did) bring the whole system down. I think you can emulate 9.2 just fine, but it's been a while since I played with this things.
fay59 5y ago
Mac OS 9 has virtual memory (it uses virtual address translation and it can swap pages to disk), but it still has a single address space that is shared between every application.
- grishka 5y ago
  Ah. I remember reading "it has virtual memory" and assumed that this includes each process running in its own address space. Was it common for applications to reach directly into kernel memory instead of using proper APIs?
Someone 5y ago
It has preemptive multitasking for compute-only tasks (the MultiProcessing library. See http://mirror.informatimago.com/next/developer.apple.com/technotes/tn/tn1176.html#mpapi http://mirror.informatimago.com/next/developer.apple.com/tec...) I also think the OS, technically, was preemptive multitasking, but ran all ‘normal’ code in a single preemptive task (https://groups.google.com/g/comp.sys.mac.programmer.help/c/fqdq59fxQ1g/m/uSy4DSDLeJcJ https://groups.google.com/g/comp.sys.mac.programmer.help/c/f...) I also vaguely remember the kernel had some memory protection enabled. Of course, almost none of that mattered for typical user-space programs.
classichasclass 5y ago
This is an issue for SheepShaver (limited to 9.0.4 because 9.1 and up require the MMU as you say), but not QEMU, which emulates the MMU and thus runs 9.2 just fine.

tambourine_man 5y ago

No, after 8.6 the system featured a micro kernel on which the old OS ran atop. I think you could opt in for better stability, but I'm not sure. But most of the OS and apps still ran on the same shared memory space with cooperative multitasking, meaning a single app could (and did) bring the whole system down. I think you can emulate 9.2 just fine, but it's been a while since I played with this things.

fay59 5y ago

Mac OS 9 has virtual memory (it uses virtual address translation and it can swap pages to disk), but it still has a single address space that is shared between every application.

grishka 5y ago
Ah. I remember reading "it has virtual memory" and assumed that this includes each process running in its own address space. Was it common for applications to reach directly into kernel memory instead of using proper APIs?

Someone 5y ago

It has preemptive multitasking for compute-only tasks (the MultiProcessing library. See http://mirror.informatimago.com/next/developer.apple.com/technotes/tn/tn1176.html#mpapi http://mirror.informatimago.com/next/developer.apple.com/tec...) I also think the OS, technically, was preemptive multitasking, but ran all ‘normal’ code in a single preemptive task (https://groups.google.com/g/comp.sys.mac.programmer.help/c/fqdq59fxQ1g/m/uSy4DSDLeJcJ https://groups.google.com/g/comp.sys.mac.programmer.help/c/f...) I also vaguely remember the kernel had some memory protection enabled. Of course, almost none of that mattered for typical user-space programs.

classichasclass 5y ago

This is an issue for SheepShaver (limited to 9.0.4 because 9.1 and up require the MMU as you say), but not QEMU, which emulates the MMU and thus runs 9.2 just fine.