Return to BSD News archive
Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!nntp.coast.net!howland.reston.ans.net!swrinde!newsfeed.internetmci.com!news.sprintlink.net!news-stk-200.sprintlink.net!news.sprintlink.net!news-dc-10.sprintlink.net!helena.MT.net!nate From: nate@trout.sri.MT.net (Nate Williams) Newsgroups: comp.unix.bsd.freebsd.misc Subject: Re: FreeBSD memory requirement Date: 20 Jun 1996 15:49:16 GMT Organization: SRI Intl. - Montana Operations Lines: 52 Message-ID: <4qbrts$sif@helena.MT.net> References: <Pine.SOL.3.93.960619222235.20516E-100000@bmec.hscbklyn.edu> Reply-To: "Nate Williams" <nate@sneezy.sri.com> NNTP-Posting-Host: trout.sri.mt.net 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. Nate -- nate@sri.com | Research Engineer, SRI Intl. - Montana Operations nate@trout.mt.sri.com | Loving life in God's country, the great state of work #: (406) 449-7662 | Montana (all the crazies are now in jail 'cept us home #: (406) 443-7063 | natives). - Fly fishing fanatic!