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Date:      Thu, 30 Oct 1997 01:18:14 +1030
From:      Mike Smith <mike@smith.net.au>
To:        Mikael Karpberg <karpen@ocean.campus.luth.se>
Cc:        dg@root.com, hackers@FreeBSD.ORG
Subject:   Re: Parity Ram 
Message-ID:  <199710291448.BAA01029@word.smith.net.au>
In-Reply-To: Your message of "Wed, 29 Oct 1997 03:29:12 BST." <199710290229.DAA07708@ocean.campus.luth.se> 

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> 
> Hmm... It's still not quite clear to me. That is, does this slow my
> computer down, in case I use ECC?

Slightly, yes.  Unless you stand over it measuring things 
microscopically, you won't notice the difference.

> 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.

It's faster and cheaper to do it inside the memory pipeline.

> 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%?

That depends; what's your system doing?  The tests we did put the 
change down in the noise (<2%) for our workload.

mike




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