Berkeley paging

[Charles Hedrick]

When discussing SV vs BSD paging, it's interesting to look at the
comparison of TOPS-20 with other DEC OS's (VMS and TOPS-10).  SV has
been compared to VMS (note that I don't know anything independent
about it, since I know only SVr2 without paging).  In many ways BSD
looks more like TOPS-20.  The claim was always made that VMS paging,
like TOPS-10 paging, was more efficient than TOPS-20 because processes
paged only "against themselves".  It always seemed that in practice,
good performance on VMS requires more adjustment of user-specific
parameters.  On TOPS-10 (where I have more detailed experience, though
years out of date), it seemed that system performance had more of a
"knee".  With one process paging, the system really did protect other
processes against it, but when several processes paged, because no
global resource computations were made, you ended up using up all the
disk bandwidth, and everybody died.  (Of course this may have improved
after I left the TOPS-10 community, which is many years ago.)  TOPS-20
definitely had more of an overhead than TOPS-10 or VMS, but required
no tuning and overloaded "soft".  One suspects something similar is
likely to be true of BSD vs. SV: that neither is universally superior,
but rather than they each have advantages in different circumstances.
It might be useful to try to characterize those circumstances rather
than decide which is "better".  Does anybody know both well enough to
have a go at it?