the pc is the main target simply because it is fairly cheap,
powerful, and readily available.

still, examples are included for other more specialised platforms in /sys/src/9:
	mtx	powerpc (PowerPC 604e)
	alphapc	Alpha
	bitsy	Compaq iPAQ H36xx, using Strongarm SA1110

3rd Edition included support for powerpc 8xx and an old mips motherboard (carrera)
as examples, and you could probably update those if you had a suitable target
and the energy.

Sparc kernel samples haven't been distributed for ages, but the contrib area
includes a 2nd edition port to Sparcstation 10/20 and LX/Classic (microsparc examples).
the distance between 2nd and 3rd/4th is greater than 3rd to 4th at this level
in the kernel, so converting them to 4th edition requires rather more work.

compiler suites are provided for the following:
          1c 68000       Motorola MC68000
          2c 68020       Motorola MC68020
          5c arm         ARM 7500
          6c 960         Intel i960
          7c alpha       Digital Alpha APX
          8c 386         Intel i386, i486, Pentium, etc.
          9c 29000       AMD 29000 family
          kc sparc       Sun SPARC
          qc power       Power PC
          vc mips        big-endian MIPS 3000 family
there are a few others that aren't in the distribution,
but could probably be got if needed.