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Comment by ThrowawayR2 | Hacker News Reader

> "Microsoft, at least, has Windows running on ARM, but it doesn't have Rosetta"

I thought that Microsoft's emulation efforts were hampered by Intel making threats, e.g. "Intel recently made an unprecedented public challenge to Microsoft and Qualcomm that basically told the latter two companies: if you ship an x86 instruction set architecture (ISA) emulator, we’re coming after you.", from https://www.forbes.com/sites/tiriasresearch/2017/06/16/intel...

If so, the blame for that really lies at Intel's doorstep as well.

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Intel has patents in things like some of the newer vector instructions still - Apple AFAIK will not translate those, and will not report them as available.

Microsoft has a performance disadvantage in that the memory consistency model of ARM is much weaker than x86 sequential ordering or x86_64s total store ordering. Apple’s chips (at least back to the A12Z) support enabling TSO per thread on the performance cores, so the translated code does not need as much fencing.

Who knows what kind of weird deals Microsoft and Intel have.

Also, Microsoft historically is awful at transitions. Look at the 64 but print driver transition - complete shitshow.

I don't think it was awful. It's not failure to 64bit transition but they simultaneously force drivers to be signed.

Did Intel similarly threaten Apple? If not, why not? Even if they didn't know for sure exactly what Apple was up to with the M1, they surely could have speculated, as so many others did.

The threat was regarding emulation. Rosetta 2 isn't emulation, it's translation.

Rosetta 2 includes both ahead-of-time translation and run-time emulation. It can run x64 jit software for example.

The jit is run-time translation still - not run-time emulation.

Can you provide a definition that specifies the difference? The end result is identical: being able to run software compiled for foreign ISA.

It doesn't emulate a whole CPU and has the simulated CPU run the code.

It translates instructions directly to the different ISA.

That is literally how performant emulators work.

At that level though, emulation/translation/simulation is blurred.

Somewhat, they're really not exclusive. You could say Rosetta is an x86 emulator that uses AOT binary translation and JIT compilation.

So why does Microsoft go the translation route instead of emulation?

Rosetta 2 is running on an Apple chip which they’ve designed to have an X86 strong memory model mode. Microsoft has to run on off the shelf ARMv8 chips.

They don't make their chips like Apple.

FWIW, the twentieth anniversary of the publication of the x86-64 specification was apparently August of this year (https://web.archive.org/web/20120308025559/http://www.amd.co... , via WP https://en.wikipedia.org/wiki/X86-64#History ), while MS announced x86-64 emulation support for ARM W10 at the end of September https://uk.pcmag.com/migrated-3765-windows-10/128922/microso... https://blogs.windows.com/windowsexperience/2020/09/30/now-m... .

Doesn't the force behind that threat depend heavily on the outcome of Oracle v Google?

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