[praecipula]

I think the largest hurdle for ARM to get over is the preponderance of Windows installations with kernels only complied for x86. Linux and OS X (Mach) already run on ARM, and I think that possibly the NT kernel runs on ARM (Windows phone 7 is ARM, right?) I have trouble seeing Microsoft port over Windows proper to ARM until there's a really strong market for it. That being said, perhaps low power consumption ARM devices will provide that market. Perhaps this is another reason that Apple has their own ARM chip - to be at the forefront of the ARM revolution, displacing MSFT?

[contextfree]

NT doesn't currently run on ARM (WP7 is still based on CE), though it was originally designed to be CPU independent. Probably the biggest obstacle for MSFT porting Windows to ARM is not the expense of the port itself, but reluctance to put out a version of Windows that's binary incompatible with all the Windows software out there.

Incidentally (and speaking of breaking compatibility), MSFT is working on a brand new kernel and operating environment (Midori) which does have ARM as a target. But this is an incubation project with no guaranteed release, though it's a very serious effort.

[nivertech]

Windows NT originally was CPU independent, but only for Little Endian architectures.

[wolfgke]

This is no problem for ARM processors since they are bi-endian (as PowerPC).

Source: http://en.wikipedia.org/wiki/Endianness#Bi-endian_hardware

[RomP]

There is nothing in Windows which requires fixed endianness. While all known versions of the OS have been shipped on little-endian machines (except XBox 360, albeit running highly modified version of NT Kernel), there is very little dependency on the endianness for all modules except format parsers and network API. Changing that is a relatively simple undertaking, much simpler than building a new version of kernel, for XBox, for example

[gecko]

That can't be correct, since I remember running Windows NT 4 on a PowerPC system.

[tesseract]

PowerPC (except PPC970 aka G5, as I recall) is bi-endian (configurable endianness); so are Alpha and Itanium which also had Windows NT ports.

[froydnj]

Alpha is most definitely not a bi-endian architecture; it's little-endian only. PowerPC chips can be either, but the vast, vast majority are big endian.

[kinetik]

Incorrect. The Cray T3E used Alpha processors in big-endian mode.

[wmf]

I don't think Windows Phone is based on NT.

Apple and Android have shown that you can build a mainstream platform ecosystem from nothing in 2-3 years, so who needs Windows compatibility?

[nl]

Neither Apple iOS or Android were "build from nothing in 2-3 years".

iOS is based on OS-X, which is based on NeXT, which is based on BSD (~40 years of work)

Android is based on Linux (so ~20 years of work)

[wmf]

My point is that they went from zero apps and zero users to lots in 2-3 years. IMO the argument that Windows backwards compatibility is the only way to get the long tail of tens of thousands of apps has been refuted.

[nl]

Oh right. Yes, I agree, then.

All a new platforms needs is a great webbrowser (which these days seems to mean "port webkit") and it's instantly viable.

[zyb09]

Didn't OSX just recently get rid of ARM support? Might be wrong though..

[vurlix]

You're confusing ARM with PowerPC, both of which are RISC architectures.

http://en.wikipedia.org/wiki/PowerPC