Date: Wed, 29 Oct 1997 03:29:12 +0100 (CET) From: Mikael Karpberg <karpen@ocean.campus.luth.se> To: dg@root.com Cc: hackers@FreeBSD.ORG Subject: Re: Parity Ram Message-ID: <199710290229.DAA07708@ocean.campus.luth.se> In-Reply-To: <199710290129.RAA20291@implode.root.com> from David Greenman at "Oct 28, 97 05:29:28 pm"
next in thread | previous in thread | raw e-mail | index | archive | help
According to David Greenman: > > > >[...Discussion on ECC/parity/no-parity memory...] > > > >I seem to recall something about partiy and/or ECC memory having slower > >access rates, or something, and therefor being a bad thing preformace-wise > >but a good thing safety-wise? > > > >I don't know where I got this, but could anyone with knowledge in the > >subject maybe enlighten me on the amount of truth behind this? > > In order to update the memory, the ECC must be recalculated over the > entire 64bit quadword. This escentially means that you have to read the > memory first, apply the changes/calculate the new ECC and then write it > back. Obviously,this makes memory writes quite a bit slower. Hmm... It's still not quite clear to me. That is, does this slow my computer down, in case I use ECC? It seems to me all this could be done on the DIMM/SIMM, or something, possibly clocked at multiple of the bus clockspeed, and therefor not effect the rate at which memory could be read/written over the bus by the CPU. If that's not the case, and the computer is actually slowed down by ECC, how much performace do you loose? 0.1%? 5%? 30%? /Mikael
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199710290229.DAA07708>