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86Box: Why Not Pentium III?

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Re: 86Box: Why Not Pentium III?

#11

Post by andrewf »

chrononaut wrote: post #6
spijdar wrote: post #5

Something alluded to, but not really elaborated on, is what the motivation is for emulating progressively newer CPUs, versus virtualizing them. With old hardware, the sort I imagine 86Box is mainly used to emulate (it's how I use it, anyway), old OSes rely on specific behavior of old systems and peripherals that can't be easily virtualized through KVM + QEMU or the like. A mixture of processors being too fast and beh…

> old OSes rely on specific behavior of old systems and peripherals that can't be easily virtualized through KVM + QEMU or the like This sounds interesting. Do you have examples of these behaviors where something is faulty using standard virtualization versus hardware-level emulation? (I know clock speed can make a difference.)

This article goes into some specifics for OS/2: http://www.os2museum.com/wp/why-os2-is-hard-to-virtualize/

Re: 86Box: Why Not Pentium III?

#12

Post by kevingadd »

billyjobob wrote: post #3

Article claims it’s not possible to emulate a Pentium III at full speed on an Apple M1, and so there’s no point to a fork attempting this feat. But isn’t that exactly what Rosetta 2 does?

Rosetta is not emulating the hardware, it's emulating the instruction set

Re: 86Box: Why Not Pentium III?

#13

Post by hulitu »

chrononaut wrote: post #6
spijdar wrote: post #5

Something alluded to, but not really elaborated on, is what the motivation is for emulating progressively newer CPUs, versus virtualizing them. With old hardware, the sort I imagine 86Box is mainly used to emulate (it's how I use it, anyway), old OSes rely on specific behavior of old systems and peripherals that can't be easily virtualized through KVM + QEMU or the like. A mixture of processors being too fast and beh…

> old OSes rely on specific behavior of old systems and peripherals that can't be easily virtualized through KVM + QEMU or the like This sounds interesting. Do you have examples of these behaviors where something is faulty using standard virtualization versus hardware-level emulation? (I know clock speed can make a difference.)

win 98 had a bug which would cause win98 to not boot on faster AMD systems.

Re: 86Box: Why Not Pentium III?

#14

Post by dusted »

AshamedCaptain wrote: post #9
dusted wrote: post #8

Earlier quoted context omitted.

The point of cycle-accurate emulation is to emulate something with accuracy down the the cycle, so that software that relies on some particularity will work on it. Performance is secondary, you can think of the emulation as a lasting documentation, which in time comes usable due to improvements of hardware and software, or can be used as a reference for FPGA, ASIC or alternative implementations.

The question is which software that requires a Pentium III also requires some CPU timing peculiarity. There have been enough CPU vendors that such software would have been difficult to run even at its era. This is not a videogame console where all hardware was the same, or the early PC world were everything was designed for the Intel 8086 timings as on the IBM PC. This is the modern PC world. Which exact CPU model wo…

Let's say I want to emulate my first SMP system, a dual p3 with windows 2000, well, without P3 (and smp) emulation, I can't.

If there was SMP P3 emulation, then I could (albeit at horrible speed, at the moment) but at some point, it'd become quite reasonable.

Re: 86Box: Why Not Pentium III?

#15

Post by AshamedCaptain »

dusted wrote: post #14
AshamedCaptain wrote: post #9

Earlier quoted context omitted.

The question is which software that requires a Pentium III also requires some CPU timing peculiarity. There have been enough CPU vendors that such software would have been difficult to run even at its era. This is not a videogame console where all hardware was the same, or the early PC world were everything was designed for the Intel 8086 timings as on the IBM PC. This is the modern PC world. Which exact CPU model wo…

Let's say I want to emulate my first SMP system, a dual p3 with windows 2000, well, without P3 (and smp) emulation, I can't. If there was SMP P3 emulation, then I could (albeit at horrible speed, at the moment) but at some point, it'd become quite reasonable.

There is SMP P3 emulation. qemu is an emulator, not a virtualizer.

There is no cycle-accurate emulation, but again the question is: why would need cycle-accurate emulation to run win2k? It runs just fine on virtualizers, even.

Re: 86Box: Why Not Pentium III?

#16

Post by lewispollard »

AshamedCaptain wrote: post #9
dusted wrote: post #8

Earlier quoted context omitted.

The point of cycle-accurate emulation is to emulate something with accuracy down the the cycle, so that software that relies on some particularity will work on it. Performance is secondary, you can think of the emulation as a lasting documentation, which in time comes usable due to improvements of hardware and software, or can be used as a reference for FPGA, ASIC or alternative implementations.

The question is which software that requires a Pentium III also requires some CPU timing peculiarity. There have been enough CPU vendors that such software would have been difficult to run even at its era. This is not a videogame console where all hardware was the same, or the early PC world were everything was designed for the Intel 8086 timings as on the IBM PC. This is the modern PC world. Which exact CPU model wo…

Isn't the point you're making the same point that the article is making?

Re: 86Box: Why Not Pentium III?

#17

Post by phire »

AshamedCaptain wrote: post #9
dusted wrote: post #8

Earlier quoted context omitted.

The point of cycle-accurate emulation is to emulate something with accuracy down the the cycle, so that software that relies on some particularity will work on it. Performance is secondary, you can think of the emulation as a lasting documentation, which in time comes usable due to improvements of hardware and software, or can be used as a reference for FPGA, ASIC or alternative implementations.

The question is which software that requires a Pentium III also requires some CPU timing peculiarity. There have been enough CPU vendors that such software would have been difficult to run even at its era. This is not a videogame console where all hardware was the same, or the early PC world were everything was designed for the Intel 8086 timings as on the IBM PC. This is the modern PC world. Which exact CPU model wo…

I'm of the belief that hardware is not truly preserved until you have a fully-accurate emulation of it.

You are correctly that software doesn't require fully accurate timings. Just accurate enough to bypass any timing bugs and replicate the experience. Especially outside of the console space. If your only goal is running all known software, then you can get away with some massive accuracy bugs.

But there is more to hardware preservation than simply running all software that might have been shipped on a platform. Some people want to do retro programming and develop new software for a platform. And if you don't have accurate emulation, then the more likely you are to introduce a bug that works in the emulator but not on real hardware. The less accurate an emulator, the more often you have to check on real hardware. And since there was such a wide variety of real hardware, your collection would have to be huge to ensure extensive testing.

You could argue that people wanting to do retro-coding as a hobby should just test on real hardware, but I'd argue that raises costs to the hobby. Also, in the distant future, the last Pentium III will die, and acquiring real hardware might not be possible. I have no idea if people will still be interesting in retro-coding for the Pentium III that far in the future, but my point is the hardware is not truly preserved unless they can.

BTW, the Pentium III was used in a console, with identical hardware configurations, so an accurate P3 might be more useful there.

Though, the Pentium III was used in a video game console. An accurate emulation could be more useful there.

Re: 86Box: Why Not Pentium III?

#18

Post by captainmuon »

spijdar wrote: post #5

Something alluded to, but not really elaborated on, is what the motivation is for emulating progressively newer CPUs, versus virtualizing them. With old hardware, the sort I imagine 86Box is mainly used to emulate (it's how I use it, anyway), old OSes rely on specific behavior of old systems and peripherals that can't be easily virtualized through KVM + QEMU or the like. A mixture of processors being too fast and beh…

What about old versions of VirtualBox? As far as I understand, VirtualBox originally used some kind of dynamic recompilation to run on hosts without modern virtualization (like VT-D). It used to run most instructions directly on the host CPU, emulating only certain ones. I think they removed it at some point, though. Is it not accurate enough? I remember it used to run OS-X much better than other virtualizers.

Re: 86Box: Why Not Pentium III?

#19

Post by cwzwarich »

It’s probably not even possible to emulate the Pentium Pro (or any other out-of-order x86 CPU) in a cycle-accurate fashion at the original speeds on contemporary hardware. Just attempting to match the original behavior for instruction scheduling, cache models, branch prediction, etc. would blow your CPU budget.
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