Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!versatc!leadsv!laic!nova!hart
From: hart@nova.laic.uucp (Howard C. Hart)
Newsgroups: comp.unix.questions
Subject: Re: Question about paging and swapping
Summary: paging/swapping in a nutshell
Keywords: paging swapping
Message-ID: <584@laic.UUCP>
Date: 13 Jun 89 20:03:47 GMT
References: <381@biophys.UUCP>
Sender: news@laic.UUCP
Reply-To: hart@nova.UUCP (Howard C. Hart)
Distribution: usa
Organization: Lockheed AI Center, Menlo Park
Lines: 29

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. I could yet not found an clear answer to this question 

As an instructor of mine very aptly put it, you're the manager of a 
company, trying to get some work done (the CPU), but all the workers
(processess) keep interrupting with their inputs/tasks that just have
to be done right away. You can try to respond to each of them one
subtask at a time (a page), then interrupt that subtask to service
another workers subtask (another page) and so on, or you can be more
efficient and service a whole worker's task at a time (swap many pages
in sequence) without allowing interruptions by other workers. This
avoids the overhead of too many changes of subject (context switches)
brought on by answering a very small portion of each worker's questions
, then moving on to the other. 
Please note, this analogy has holes in it big enough to drive a tank
through, but you did ask for a clear description. As for relative
performance, I'll give you the party line...it depends on the
size of the application and other factors. The above explanation should
give you a first cut at which method shows higher performance. Swapping
is usually better, but if you could fit many processes on one page each,
the inherent overhead in swapping would make it slower than paging.


Howard C. Hart                  UUCP:{sun!sunncal,pyramid}!leadsv!laic!nova!hart
Lockheed Missiles and Space Co.
Orgn 59-53, Bldg 593            Ph: (408) 743-2253 or -7353
Sunnyvale, CA 94086