On Tuesday 13 June 2006 14:23, Rick Kelly wrote: > Johnny Billquist said: > >> There's actually a cheesy way to do demand paging with microprocessors > >> that don't support demand paging (such as the original 68000--another > >> "16 bit" machine). The way to do this is to run two processors in > >> parallel but skewed by one instruction. If the first one does a bad > >> memory fetch, then the second one will not have fetched the instruction > >> causing the fault so contains restartable machine state. Masscomp sold > >> a machine like this once. > > > >Didn't the first Apollos do this? > > And also the Sun 1.
IIRC it was simpler than that. When the first cpu caused a 'miss' it was put in wait and cpu 2 handled the pagein and then released cpu 1. Keeping the two cpus synched, one instruction apart would have been too complicated if not impossible...
