Do not criticise crufty old BIOS or Garry Kildall too much.

x86 boot up in real mode and this was the only mode the original PC had.

With a 1 MiB address space DMA transfers must be less that this.
You could do a useful "OS" that leaves the real OS INT 15h BIOS running in virtual 8086 mode while your MPI (IEEE 1003 Unix) runs in protected mode.

Effectively F...ed Itannic is just plain mad like Rube Goldberg and Heath Robinson x86 processors. BIOS is better.

Garry Kildall allowed for reentrant drivers which exist in the ripped MeS-DoS driver API, but these were not useful in slow Z80 and 8088 CPUs of the day.

The OLPC XO uses standard IEEE 1275 firmware.

This has an AMD Geode CPU which is not full x86 with sse, but runs generic x86 mmx binaries. Freescale have better POWER solutions than x86.

This runs it's own Red Hat based system.

I have not yet got it to boot (debootstrap) stock Debian kernels with <http://packages.debian.org/sid/grub-ieee1275>
yet as treading water doing other things.

Playing with SunBlade 6000 with UltraSPARC T2 and new IBM POWER6 for work. Real computers are much more rewarding than PeeCees.