[pups] Forks under V6

[Norman Wilson]

I believe the practice John Holden describes from Mini-UNIX (only one
process in memory at a time, hence a context switch is the same as a
swap) was also part of the very earliest UNIXes, on the PDP-7 and the
11/20, neither of which had hardware memory management.  Dennis Ritchie's
`Evolution of the UNIX Time-Sharing System' paper (in the October 1984
Bell Labs Technical Journal, the second issue to be devoted entirely to
UNIX), tells how it worked in some detail.  It wouldn't surprise me if
the swap-to-fork mechanism lived on for a while even after the system
learned about memory management, but I don't actually know that.  (Warren:
wbat does the old system you have do?)

Anyone who wants to verify what John describes for V6 can look in (among
other places) the Lions book; newproc is at line 1826, at the beginning
of slp.c.

Norman Wilson

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