NT and ARM
NT (and Win7 is NT 6.1.xxxx, first version was NT3.1 in 1993) had at various stages:
386 (won't run on 386 now)
pentium Pro + PAE (Win9x was like a dog on this and killed the Pentium Pro)
DEC 64bit Alpha (NT4.0)
NT4.0 was last version to run loads of non x86
In the 1990 to 1996 era the ARM wasn't very suitable for NT.
However ARM has always been the main cpu for CE (spawning Phone, Auto, Mobile Editions). At one stage ARM became the only supported CPU for Mobile or CE.
"Embedded" Windows is confusing. There are three incompatible families
1) CE based and runs on ARM, There is a version 7. A GUI was optional
2) NT based (NT4.0 was best). There is a version 7. used to Support MIPS and PowerPC, now only x86-x64. A GUI was optional
3) Win 3.x/DOS based. 386 or more (maybe 286 possible) . Killed recently.(Last Autumn?) Used POS and ATM.
The original issues with ARM in 1990 to 1996:
Though technically a 32bit CPU, in some respects more like a 16 bit RISC. Thumb-2 in 2003 added more 32bit goodness
Originally no 16 bit type. Not good for Porting Windows efficiently.
Originally No MMU
Originally No FPU (not actually a huge issue)
Current higher end ARM could run a ported version of Windows NT. Rumour is that the reason some bits of Win2K, XP, Vista and Win7 are the same is because MS doesn't have the source. Only x86 binary. I don't believe this myself.
Tux knows how to run on ARM, MIPs, x86, x64 and few other things... It's those happy feet.