OS4 Classic, why disable the 68k ?

[Piru]

The Phase5 accelerator card has only one memory bus so it CANNOT run both processors at the same time.  It can switch between them, but not run them in parallel.

The CPUs most definitely do run in parallel.

I don't know who invented this nonsense and for what purposes, but it is not true.

[Piru]

Really? I don't think it worked that way.

It was possible to run 68k and PPC code independent from each other, at least with PowerUP. There were certain highly optimized apps that used to do this. For instance the infamous FastQuake used a special cache inhibited memory area as a ring-buffer to avoid the need for cache flushes. This way both CPUs could run at full speed with as few context switches as possible.