🚀 go-pugleaf

In article <2383@peora.UUCP> joel@peora.UUCP (Joel Upchurch) writes:
>
>	Another consideration, is that on at least some virtual
>	memory systems I've worked with, the the system transfers
>	the program over to some sort of paging file, before it
>	starts, which means that you end up reading the whole
>	program in anyway, and writing it out to boot. Does anyone
>	know of a virtual memory system that doesn't work this
>	way?
>

Yes! AT&T UNIX System V (at least the demand paging versions).

In the default case (413 magic number -- demand loaded file &
no sticky-bit set) System V demand-pages the program directly 
from the file system. Text (code) pages and unmodified data pages
never get written to any paging device. 

Of course, one reason for all this is that this system runs
on 3b2 computers with small disks and this scheme reduces the 
amount of swap space required.

System V also effectively uses all available main memory pages 
as a cache for the text and data pages on disk (separate from
the file system buffer cache).  This means, for example, that
on a large single-user workstation, when you compile a program the 
first time the compiler must be loaded from the disk.  But, if you
edit and re-compile, the compiler's pages are still in memory and
will be re-used without going to the disk. 

Reuel Nash
MIPS Computer Systems, Inc.
930 E. Arques 
Sunnyvale, CA 94086
408-720-1700 x244
decwrl!mips!reuel

#include <std.disclaimer>