Path: utzoo!attcan!uunet!mcsun!ukc!edcastle!ngse18
From: ngse18@castle.ed.ac.uk (J R Evans)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Quien es mas macho? (HD caching)
Message-ID: <6948@castle.ed.ac.uk>
Date: 31 Oct 90 10:16:00 GMT
References: <1990Oct27.162723.2834@doe.utoronto.ca> <13510003@hplsla.HP.COM> <1990Oct30.220831.17172@math.lsa.umich.edu>
Organization: Edinburgh University Computer Services
Lines: 31

hyc@math.lsa.umich.edu (Howard Chu) writes:

>Hm. With sufficient memory and a good cache, isn't the whole idea of a
>RAMdisk pointless?

Not in all cases (and that's true, even on machines with virtual
memory).  To take the example of compilation: most compilers produce a
significant number of temporary files at various stages, which persist
for only a few seconds before they are deleted.  [GNU cc is an exception
here - this is one of the reasons it's a memory hog].  At the same time,
to the best of my knowledge, all the software caches for the ST are
'write-through'.  This means that all files are actually written out
to disk as they are made.  [Again, if there are 'intelligent' caches out
there, given TOS's insecurity, *I* wouldn't risk my data by using them
in a development environment].  So, during a typical compilation, even
though a cache will generally give an improvement in runtimes over no
cache, use of a RAM-disk for temporary files will (except in some
*very* particular cases) be even faster.  

The choice as to whether to use a cache and/or a RAM-disk is very
dependent on the particular work being performed.  Especially on a
single user machine like the ST, the appropriate choice will probably be
different for the same user on different occasions [I certainly adjust
these choices on my ST system - often several times within a session].  
This is an example of system tuning.  As an illustration of how bizarre
it can get, I have an old PDP-11 which is largely used for program
development.  Of 4Mb memory, 3Mb is used as a RAM-disk, 740k as disk
cache, and only 256kb as system memory space - odd, but that's the way
it functions best *for that application*.

Russ