49

I've been trying to find more information about non-Intel versions of Windows NT regarding x86 emulation but found very little about it. There is one sentence about it in the Wikipedia page but the reference link is gone.

Was there any sort of x86 emulation on MIPS, PowerPC or Alpha versions of Windows NT?

phuclv
  • 3,592
  • 1
  • 19
  • 30
Eric Cartman
  • 6,760
  • 5
  • 35
  • 59

2 Answers2

64

There was x86 emulation on Windows NT, on MIPS, Alpha, and PowerPC — in fact, more than x86 emulation, PC emulation. The operating system itself ran natively, and applications could be built natively as well; but for a non-x86 port to be viable, it had to be able to run existing x86 programs.

The Alpha release of Windows NT was quite famous at the time for using a binary translator rather than a “plain” emulator, FX!32, developed by Digital; it would run x86 programs, keeping track of which parts of the binaries were actually used, and then translate them to Alpha instructions and store them in DLLs which were used the next time the programs were run. FX!32 was described in a fair amount of detail in various publications at the time, see this USENIX paper and this Digital Technical Journal article.

On MIPS and PowerPC (and Alpha for DOS x86 programs), NTVDM.EXE could emulate a PC as well, using a version of Insignia’s SoftPC (which was common on workstations at the time). This post on Virtually Fun looks at the MIPS version specifically.

The scope of these tools is different: FX!32 translates Win32-on-x86 to Win32-on-Alpha, whereas SoftPC emulates a complete 486-level PC. (Even though Alpha was always 64-bit, publicly-available versions of Windows NT were 32-bit only.)

Stephen Kitt
  • 121,835
  • 17
  • 505
  • 462
  • Thank you for the links. Lesefutter :)) It's maybe worth to add that these emulations where more intended for copatibility reasons with existing applications, as applications could be (and would) compiled to native code. – Raffzahn Jan 26 '19 at 12:09
  • 6
    After Intel bought the Alpha technology, FX!32 became the basis for the x86 emulation for IA-64, I believe. Interestingly, around the same time, Alpha technology showed up in both major vendors's products: AMD's new frontside bus at that time was based on the FSB of the canceled EV8. – Jörg W Mittag Jan 26 '19 at 15:39
  • 3
    The comment about the alpha doing binary translation is not strictly true, unusually for a CPU, the alpha allowed the OS to load different microcode, and, at least some, of the x86 emulation was done in the CPU itself using this technique. The contemporaneous linux kernels have the gory details, if you're interested. Better still the Alpha boot rom (like the BIOS) could also use this feature so regular x86 option roms (like SCSI controllers, and video bioses) worked on an Alpha systems. – james Jan 26 '19 at 20:24
  • @james I’m not sure I understand — are you saying that FX!32 didn’t do binary translation? Which comment are you referring to? – Stephen Kitt Jan 26 '19 at 21:18
  • 2
    @james are you referring to PALcode by any chance? As I understand it (and the last time I talked to an Alpha designer about this was twenty-odd years ago, so I might be wrong), PALcode is used to handle system initialisation, context switching, interrupt dispatching, cache management etc.; while it can take care of some instruction emulation, that’s intended for the optional instructions in the Alpha architecture, not for emulating a different architecture altogether. – Stephen Kitt Jan 27 '19 at 15:45
  • @james Windows NT did have its own PALcode, but I suspect this had more to do with the different system call expectations (compared to VMS or Digital Unix) and the NT developers’ decision to treat Alpha as a 32-bit CPU rather than a 64-bit CPU (at least, viewed from user space), rather than implementing x86 support in PALcode. – Stephen Kitt Jan 27 '19 at 15:46
  • 1
    @StephenKitt - I spun up an old tape cartridge looking for the source of em86 and libem486.a but didn't find it (that was the linux helper binary that was syscall compatible with ia32) - I dimly remember a paper about how they'd cunningly added palcode instructions to do some of the x86 emulation, there are some alpha greybeards around here - I'll ask them. – james Jan 27 '19 at 15:53
  • @james ah yes, the secret libem486.a! I don’t think that was used on Windows NT though, was it? Although I imagine if PALcode was used to help libem486, I imagine something similar could be used to help x86 emulation on NT ;-). – Stephen Kitt Jan 27 '19 at 16:05
  • 4
    Just for what it's worth, FX!32 was effective enough that for a while, the fastest way to run some x86 Windows programs was under NT 4 on an Alpha (assisted, of course, by the Alpha's much higher clock speed). – Jerry Coffin Mar 23 '19 at 17:19
  • publicly-available versions of Windows NT were 32-bit only Windows 2000 64-bit for Alpha AXP has just been leaked not so long ago – phuclv Jun 11 '23 at 16:21
  • FX!32 did not appear until Alpha NT had been around for a while. Before then, it emulated an x86 PC in the same way as MIPS and PowerPC did it. – John Dallman Jun 11 '23 at 21:34
  • An excellent way to mess up an Alpha NT4 machine was to install the x86 version of Active Desktop on it. This did run, thanks to FX!32, but it was astonishingly slow. – John Dallman Jun 11 '23 at 21:36
3

Here's a screenshot on Windows NT for Alpha showing x86 emulation support

Windows NT on Alpha x86 emulation option

See Exploring Windows 2000 on Alpha together with YOU

It uses FX!32 for emulation

FX!32 is a software emulator program that allows Win32 programs built for the Intel x86 instruction set to execute on DEC Alpha-based systems running Windows NT. Released in 1996, FX!32 was developed by Digital Equipment Corporation (DEC) to support their Alpha microprocessors.

FX!32 version screenshot

FX!32 optimization screenshot

Regarding x86 emulation on PowerPC some information can be found in Installing Windows NT 4.0 On A PowerPC

phuclv
  • 3,592
  • 1
  • 19
  • 30