E wrote in message ...
This is where it gets interesting. Why doesn't Microsoft have an x86-64
version ready of Windows XP?

Set your wayback machine to the early-mid-90's and remember that Microsoft
sold Windows NT for a 64-bit platform (Alpha) before. Rumors have it that
other RISC platforms were targets back then too. Clearly they have (or
had) some internal experience with multiple target platforms, even though
it's not nearly as extensive as the Linux experience.

Back then the big gotcha was binary-only driver distributions that weren't
cross-compatible. Microsoft invested a lot of time and money into some
mitigation schemes, some of which were clever or stupid depending who you
ask (virtualized 386 on an Alpha handling driver stuff!) but all that
may have to be re-done... AGAIN. Linux doesn't suffer nearly so much
from this stupidity (but it does, to some extent, as many manufacturers
distribute binary-only drivers for Linux. That's not the fault of Linux,
although many regard binary-only drivers as pure evil.)

Tim.