Newsgroups: comp.periphs
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Hard drive speeds
Message-ID: <1989Aug29.040250.23754@utzoo.uucp>
Organization: U of Toronto Zoology
References: <17640@ut-emx.UUCP> <16567@pasteur.Berkeley.EDU> <6987@sdcsvax.UCSD.Edu> <1989Aug28.050055.28526@utzoo.uucp> <13700@brunix.UUCP>
Date: Tue, 29 Aug 89 04:02:50 GMT

In article <13700@brunix.UUCP> sgf@cfm.brown.edu (Sam Fulcomer) writes:
>>Somebody's been reading old papers... Very few modern Unixes swap.  Paging
>
>In the modern Unixes which I know about processes are born with a swap. Other
>swapping (during normal scheduling) depends on the implementation of the
>scheduler, but they (as far as I know) all do it. 

"What we have here is a failure to communicate." :-)

The "swapping" that many modern Unixes do has little or nothing to do with
the "swapping" that old ones did.  Old-Unix swapping was moving the whole
process to or from disk as a unit.  Modern-Unix swapping is deciding that
we aren't going to run this guy for a while so we'll let his in-core pages
go.  The terminology has remained although the implementation has changed.
Old-Unix swapping put a premium on data-transfer rate but made seek time
a secondary issue.  Modern-Unix swapping has nothing in particular to do
with disk i/o characteristics, since it's the paging subsystem that does
all the actual disk i/o for memory management.

I do not doubt that there are many vendors still shipping old Unixes.  Utzoo
ran such a system until last summer.  That does not make them any less old
or any more deserving of the adjective "modern".  Kerosene lamps are still
made, but they are not usually considered modern.
-- 
V7 /bin/mail source: 554 lines.|     Henry Spencer at U of Toronto Zoology
1989 X.400 specs: 2200+ pages. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu