Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uwm.edu!zaphod.mps.ohio-state.edu!usc!ucsd!nosc!humu!pegasus!richard
From: richard@pegasus.com (Richard Foulk)
Newsgroups: comp.unix.i386
Subject: Re: ESDI caching disk controllers: Reprise
Keywords: ESDI cache
Message-ID: <1990May3.050416.14124@pegasus.com>
Date: 3 May 90 05:04:16 GMT
References: <274@caslon.cs.arizona.edu> <873@sixhub.UUCP> <1424@ssbn.WLK.COM> <1736@serene.UUCP> <263E613E.23840@paris.ics.uci.edu>
Reply-To: richard@pegasus.UUCP (Richard Foulk)
Organization: Pegasus,  Honolulu
Lines: 21

>> With a 768K cache memory on one card I routinely get 32% cache hits
>> and with 4Mb on the one in ssbn I get 48-52% cache hits.
>
>I have never understood this.  If a caching disk controller with 4Mb gives
>you a high hit rate, why not put the 4Mb of RAM into your CPU, and
>let UNIX use it as a cache?  The hit rate should be the same.
>The win is that the OS should be able to divide the RAM between disk
>cache and process space (I assume UNIX isn't brain-dead in this regard?).
>Then you have the best of both worlds.

I have vague recollections of several different sets of research into
the disk cache versus more main-memory question using Unix.  Adding to
main memory almost always won out as I recall -- at least with proper
tuning.

The disk cache is certainly a win with MESS-DOS since it doesn't have
any idea what to do with more memory.  I think that's where these
boards are coming from.

-- 
Richard Foulk		richard@pegasus.com