[wtallis]

It would be more like the OS 9 -> OS X switch happening at the same time as the PPC -> Intel transition, but without the old CPU architecture being totally deprecated.

Apple's notable for having made 3 major transitions (68k to PPC, MacOS to OS X, and PPC to Intel), but all three of those were as minimal as they could be given the circumstances. The architecture transitions were made with almost completely transparent binary compatibility and minimal changes needed for source code, while the source-incompatible OS/API change was made as gradual as possible with a long grace period (which a few companies chose to exploit rather than update their apps before it was too late).

Windows as a system is clearly not clean enough at the moment to easily switch architectures without needing a lot of complex compatibility stuff thrown in. If they try to force developers off old APIs and introduce a new architecture, that new architecture will be a second class citizen and will need a lot of external factors to give it traction.

[brudgers]

>"Windows as a system is clearly not clean enough at the moment to easily switch architectures without needing a lot of complex compatibility stuff thrown in."

Windows currently runs on two radically different architectures...x86/x64 and Itanium. It has for more than nine years.

http://en.wikipedia.org/wiki/Itanium#Architecture

http://en.wikipedia.org/wiki/Windows_XP_editions#Windows_XP_...

[steveb]

It may run on Itanium, but it doesn't support more than a fraction of the x86 server functionality.

http://technet.microsoft.com/en-us/library/cc772344(WS.10).a...

I don't see how Microsoft will ever shed the x86 legacy in Windows. Intel would have an interest in killing off arm-based laptops with aggressive pricing, and there really isn't any history of Windows developers rebuilding apps to support other chip architectures.

[wtallis]

Wow, that's a sad list. It looks like they didn't even port half of the server components to the Itanium, and they warn you not to use .NET for anything performance-sensitive. The closest thing they've got to a modern, portable environment and their first port of it is so embarrassingly slow that they have to warn you on the feature list. Even worse, their modern GUI APIs (WPF) weren't ported at all, so even simple .NET apps are at risk of not working due to not using an archaic GUI toolkit.

Clearly the NT kernel is quite portable. There's plenty of evidence of that (MIPS, PPC, Alpha, IA-64... ). But there's no evidence that even the most modern and supposedly portable components of the desktop experience are actually at all portable. Hardly any of it has (as far as we know) actually been ported.

[xpaulbettsx]

There's no reason all of that stuff couldn't run on Itanium too, but it's a matter of choosing what to invest in; OS releases have a huge test cost with supporting anything, and Itanium is too small a market - ARM is different because it's clearly consumer-based and it's here to stay. I assure you, it is all portable.

[kurtsiegfried]

This is true, although unfortunately Server 2008 R2 will be the last version of Windows to support Itanium:

http://blogs.technet.com/b/windowsserver/archive/2010/04/02/...

Although the article indicates that support will be rolling around for a while.

[duskwuff]

It's also run on Alpha in the past, but both the Itanium and Alpha ports are pretty thoroughly marginalized at this point.

[rbanffy]

And MIPS, PowerPC...

And lets not forget i860 and the Intergraph Clipper.

[blub]

Do you have personal exprience with the Windows kernel and user space code base? If so, what makes it unclean?