On Jan 22, 2008, at 8:54 PM, Rick Thomas wrote:
The rule of thumb comes from UNIX days (BSD and even before that
with AT&T UNIX). In order to be completely sure you would be able
to swap out a program when memory became full, UNIX allocated a page
of swap for every page of virtual memory a program occupied. So if
vi required 256K to run, there was 256K of swap space allocated to
it. The 2 to 1 ratio came from the observation that a busy UNIX
time-sharing system with lots of users ran most of it's time with
half the users doing something that required CPU/memory resources
and the other half thinking, so you could afford to overcommit
memory by a factor of two.
Thanks for the interesting history lesson. :)
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