6 ms·

Yeah... both QEMU and Bochs have long been able to emulate a full x86 system. QEMU at least has had some people boot x86 macOS under emulation, but it hasn't be

Yeah... both QEMU and Bochs have long been able to emulate a full x86 system. QEMU at least has had some people boot x86 macOS under emulation, but it hasn't been that interesting until now, since on x86 running macOS under a VM has been more useful.

ineedasername 6y ago
About 8 years ago, the last time I tried QEMU, it was painfully slow. With 8 years more development & much faster hardware, it should be relatively smooth. In general it seems like emu tech keeps up with the desire for its use.
- brigade 6y ago
  To be fair, full-system emulation is still going to be pretty slow; emulating an MMU is painful and it's not going to be any easier when you can't use 4k pages.
  - twicetwice 6y ago
    Oh, this is very interesting—I just finished the Virtual Memory assignment for my Operating Systems class. (We had to use Bochs, and it was slow.) Why is emulating an MMU particularly painful?
    - avhon1 6y ago
      It adds a layer of indirection (which has to be intercepted and emulated) for every single access to RAM.
    - ineedasername 6y ago
      Just curious, what OS were you using with Bochs? Last I used it around 8-10 years ago, playing around with Win95. It was painfully slow then, unusable, but I'd be curious about the level of improvement: was it minimally usable?
      - twicetwice 6y ago
        The one we wrote for the class :) Well, sort of. The first assignment was to write a bootloader in x86 assembly. For the second assignment we were given a bootloader and a partially-implemented kernel, and we had to finish the kernel by writing a non-preemptive (cooperative) scheduler (including implementing context switching and so on). Third assignment same thing but a preemptive scheduler. And so on. The partially-implemented kernel is very rudimentary—kernel threads but no userspace threads or forking, no filesystem, no virtual memory and no actual difference between kernel mode and user mode (until the virtual memory assignment, in which the partial kernel we were given did actually do ring transitions), etc. Anyway all this is to say that we were running a very very bare-bones, stripped-down kernel, and even then it was annoyingly slow, so I expect that it would be still be extremely slow running a "real" OS. It's my understanding that that's not really what Bochs is for, though. If you want to run Win95 use a normal VM; Bochs is meant to be a low-level x86 development tool. Though again that's just my impression, so I could be wiong in that.

ineedasername 6y ago

About 8 years ago, the last time I tried QEMU, it was painfully slow. With 8 years more development & much faster hardware, it should be relatively smooth. In general it seems like emu tech keeps up with the desire for its use.

brigade 6y ago
To be fair, full-system emulation is still going to be pretty slow; emulating an MMU is painful and it's not going to be any easier when you can't use 4k pages.
- twicetwice 6y ago
  Oh, this is very interesting—I just finished the Virtual Memory assignment for my Operating Systems class. (We had to use Bochs, and it was slow.) Why is emulating an MMU particularly painful?
  - avhon1 6y ago
    It adds a layer of indirection (which has to be intercepted and emulated) for every single access to RAM.
  - ineedasername 6y ago
    Just curious, what OS were you using with Bochs? Last I used it around 8-10 years ago, playing around with Win95. It was painfully slow then, unusable, but I'd be curious about the level of improvement: was it minimally usable?
    - twicetwice 6y ago
      The one we wrote for the class :) Well, sort of. The first assignment was to write a bootloader in x86 assembly. For the second assignment we were given a bootloader and a partially-implemented kernel, and we had to finish the kernel by writing a non-preemptive (cooperative) scheduler (including implementing context switching and so on). Third assignment same thing but a preemptive scheduler. And so on. The partially-implemented kernel is very rudimentary—kernel threads but no userspace threads or forking, no filesystem, no virtual memory and no actual difference between kernel mode and user mode (until the virtual memory assignment, in which the partial kernel we were given did actually do ring transitions), etc. Anyway all this is to say that we were running a very very bare-bones, stripped-down kernel, and even then it was annoyingly slow, so I expect that it would be still be extremely slow running a "real" OS. It's my understanding that that's not really what Bochs is for, though. If you want to run Win95 use a normal VM; Bochs is meant to be a low-level x86 development tool. Though again that's just my impression, so I could be wiong in that.