Microsoft built Windows CE for MIPS, in the first instance, on NEC's
Vr4xxx microprocessors (which in turn are pretty much compatible with
the vintage 1990/91 MIPS R4000).
In an entertaining inversion of the standard economics, it's much
cheaper to redesign a microprocessor than to get Microsoft to port
an OS. So 1998/99 saw a spate of announcements of MIPS CPUs
featuring "R4000 compatibility".
What it meant is "we hope that Windows CE runs on this".
WinCE has not (so far) been quite such a large market as the MIPS
But this a MIPS tradition: more than ten years ago the false prospect
of huge sales for Windows NT on MIPS inspired companies to invent some
MIPS CPUs which (after their intended market proved illusory) went on
to power Cisco routers, Nintendo 64 consoles and HP laser printers.
Windows CE might leave a similar legacy for Linux/MIPS. Before the
great WinCE enthusiasm low-cost MIPS CPUs often lacked memory
management and suffered from much pointless and troublesome
divergence. But now, if you've got a Linux port which is based on
32-bit code and runs on an R4000, it extends fairly easily to most