Pragmatically, windows runs on a single Architecture.
Sure, there's been editions for other architectures, but they're more anecdotal experiments than something usable.
I can go out and buy several weird ARM or PPC devices and run Linux or OpenBSD on them, and run the same stuff I use on my desktop regularly (except Steam).
The fact that windows relies on a stable ABI is it's major anchor (while Linux only guarantees a stable API).
they're more anecdotal experiments than something usable
Wrong. Microsoft explicitly set out multi-architecture support as a design goal for NT. MIPS was the original reference architecture for NT. Microsoft even designed their own MIPS based systems to do it (called 'Jazz'). There was a significant market for the Alpha port, especially in the database arena, and it was officially supported through Windows 2000. They were completely usable, production systems sold in large numbers.
In the end, the market didn't buy into the vision. The ISVs didn't want to support 3+ different archs. Intel didn't like competition. The history is all pretty well documented should one take the time to learn it.
Except they did, though apparently you missed it. MIPS was the original port. Alpha was supported from NT 3.1 through Windows 2000, and only died because DEC abandoned the Alpha, not that Microsoft abandon Alpha (it was important to their 64-bit strategy). Itanium was supported from Windows 2003 to 2008R2. Support for Itanium only ended at the beginning of this year, once again because the manufacturer abandoned the chip.
I'm sure you can redefine "achieve" to exclude almost 17 years of support (for Itanium), if you're that committed to being right. Heck, x86-64 support has "only" been around for 20 years or so. Doesn't make it right.
well, for some things. fx32 for the apps people wanted though was deficient. The NT3.1-era Alphas didn't have byte-level performance so things like Excel, Word, etc. all ran terribly, as did Emacs and X. I supported a lab of Alphas running Ultrix and they were dogs for anything interactive and fantastic for anything that was a floating point application.
People forget that at launch Windows NT ran on MIPS & DEC Alpha in addition to x86. The binary app issue was a killer for the alternative archs.