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Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!news.rmit.EDU.AU!news.unimelb.EDU.AU!munnari.OZ.AU!spool.mu.edu!howland.reston.ans.net!swrinde!elroy.jpl.nasa.gov!news.msfc.nasa.gov!newsfeed.internetmci.com!news.itjit.ad.jp!news.iij.ad.jp!news.CET.CO.JP!usenet From: Li Zhengchun <lilyli@cet.co.jp> Newsgroups: comp.unix.bsd.freebsd.misc Subject: Re: FreeBSD memory requirement Date: Sat, 22 Jun 1996 14:43:43 +0900 Organization: CET Lines: 51 Message-ID: <31CB880F.7D28@cet.co.jp> References: <Pine.SOL.3.93.960619222235.20516E-100000@bmec.hscbklyn.edu> <4qbrts$sif@helena.MT.net> NNTP-Posting-Host: a11m.cet.co.jp Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 2.0 (Win95; I) Nate Williams wrote: > > In article <Pine.SOL.3.93.960619222235.20516E-100000@bmec.hscbklyn.edu>, > David Zakai <zakaid99@hscbklyn.edu> wrote: > >Proposed hardware for new FreeBSD setup: > > > >laptop > >486 DX2 50MHz > >8 Meg RAM, 128k cache > >IDE hard disk 350 Meg > >Adaptec APA-1460 SlimSCSI PCCard > >Iomega JAZ drive > > Is the JAZ drive the SCSI version or the parallel version? Also note > that the current FreeBSD sources don't *yet* support the SlimSCSI card. > I'm slowly integrating the code from the Nomad PCCARD distribution as I > understand it. > > >Although I understand that FreeBSD will run with less memory, > >I am considering adding more (total 12 Meg or 20 Meg RAM). > >A recent email message indicated that more memory may not > >improve performance greatly because of hardware cache size. > > I have no idea how much cache I have on the laptops I have access to, > but more memory is generally a good thing. You should be able to handle > 16MB with that much cache w/out problems. > > >I don't understand this concept. I thought that the > >main RAM memory could be used for cache. > > The recent email was talking about 'hardware' cache, vs. software cache. > PC hardware (generally) has two levels of hardware cache. L1-cache is > on-chip, L2-cache is on your motherboard, both make it appear that your > main memory is faster than it is. If you have more memory main memory > than can be effectively 'cached' inside of the L2 cache, then it's > possible that your system could be slower than with less memory because > the cache is ineffective, thus making *all* memory accesses appear to be > at the slower main-memory speed. > > This is completely different from the software cache that Unix uses for > programs and disk caching. > > Hennessey & Patterson's book on hardware architecture is a great book > for explaining the effects of hardware caches and the like. If you're > interested pick it up at any decent techincal bookstore which should > have it in stock. How's does Schimmel's "Unix for Modern Architectures" fair with Hennessey & Patterson? -mh