Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cmcl2!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.unix.questions
Subject: Re: Question about paging and swapping
Keywords: paging swapping
Message-ID: <10393@smoke.BRL.MIL>
Date: 11 Jun 89 04:59:01 GMT
References: <381@biophys.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 21

In article <381@biophys.UUCP> ruba@biophys.UUCP (Rudolf Baumann) writes:
>I would like a clear description about the difference of paging and 
>swapping and which of both has more influence on the performance of
>a system.

There are a lot of variations, but the basic distinction is that
an entire process space is swapped out, while only a segment of a
process is paged out to backing store.  Other things being equal
(which they usually aren't), paging evidently involves less work
for the operating system and consequently should be more efficient.

In actual practice, if the job mix demands much more main memory
than is actually available, simplistic implementations of both
swapping and paging are likely to lead to severe thrashing and
consequent overall system inefficiency.  Additional cleverness is
required in the system memory allocation and scheduling algorithms
to overcome this tendency.

It's a bit strange that you couldn't find a discussion of this
in an operating system design book; I would have thought that it's
a standard topic.