In message <v04220800b6eac5f4b2a9@[216.240.50.19]>"Erik E. Fair" writes:

>There was a time when UNIX did not page - it swapped. Processes were 
>either all the way in RAM, or not there at all - no "pages" at all. 
>On that sort of system, there is no need to support restartable 
>instructions for page faults.

Yep. But these days "Unix" includes forget mmap(), copy-on-write
semantics, and other address-space-sharing mechanisms which, in
general, are not implementable using swapping.

(c.f. Minix on the 8086, or Mini-Unix on PDP-11/10s.)