Date: Sat, 25 Oct 1997 18:12:50 -0400 From: Jerry Hicks <wghhicks@ix.netcom.com> To: "Žoršur Ivarsson" <totii@est.is> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Parity Ram Message-ID: <34526EE2.64DE0BA6@ix.netcom.com> References: <Pine.BSF.3.96.971025115335.173A-100000@trojanhorse.ml.org> <34524948.41C67EA6@est.is> <34525F3B.1137B612@ix.netcom.com> <345267BF.167EB0E7@est.is>
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Yeah, but when you go to buy memory they have ECC *OR* parity types available. ECC generally costs more than parity... i understand the way ECC works, the minicomputer systems i've worked with in days past held 3 bits for every 8. Just wondering what parity RAM *really* means (these daze). WRT the reason parity could be worse, most of the schemes i'm familiar with use only a single bit per eight bit quantity. Parity bits can be bad too, that is why most ECC schemes are considered superior (to me anyway). Off to find Hamming's proof... Cheers! Jerry Hicks, jerry_hicks@bigfoot.com Žoršur Ivarsson wrote: > > Jerry Hicks wrote: > > > > Žoršur Ivarsson wrote: > > > > > > This has helped me several times when I was suspecting broken memory in > > > the old days (90-93) :-) > > > > > > Thordur Ivarsson > > > > ECC Memory was marginally useful for this years ago when were using NMOS > > RAM. Lately, most memory failures I've seen are catastrophic, taking out > > a whole device or better. > > > > I'm not a hardware specialist; Does 'Parity RAM' employ a conventional > > parity scheme, a la asynch serial communications? > > > > Didn't Richard Hamming show these to -cause- more problems than they > > solve? It seems I recall a number like 256K (bits/bytes/words?) as being > > the threshold in a proof he presented. > > > > Jerry Hicks > > jerry_hicks@bigfoot.com > > In the old days 8088, 8086, 80186, 80286 and 80386 it was just plain odd > or even > parity like in serial communications but later on came better algorithm > that could > really fix wrong bits > > Thordur Ivarsson
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