From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 10 May 2001 18:45:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 10 May 2001 18:45:04 -0400 Received: from neon-gw.transmeta.com ([209.10.217.66]:22803 "EHLO neon-gw.transmeta.com") by vger.kernel.org with ESMTP id ; Thu, 10 May 2001 18:44:56 -0400 To: linux-kernel@vger.kernel.org From: hpa@transmeta.com (H. Peter Anvin) Subject: Re: Wow! Is memory ever cheap! Date: 10 May 2001 15:44:10 -0700 Organization: Transmeta Corporation, Santa Clara CA Message-ID: <9df5jq$8dq$1@tazenda.transmeta.com> In-Reply-To: <200105090424.AAA05768@soyata.home> <20010508222210.B14758@work.bitmover.com> <3AF9B0D2.F2E330F9@gmx.de> Reply-To: hpa@transmeta.com (H. Peter Anvin) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Disclaimer: Not speaking for Transmeta in any way, shape, or form. Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Followup to: <3AF9B0D2.F2E330F9@gmx.de> By author: Edgar Toernig In newsgroup: linux.dev.kernel > > I think you have a wrong idea why the ECC is there. ECC deals with > the inherit shortcommings of DRAM. > > DRAMs are not perfect. They have a probability to lose a bit. > Normally this probability is low enough to live with it. Lets say > you have a system with 1MByte and let's say the probability for a > single bit error is around 1 error in 100 years. Good enough. > Now put 1GByte in the system. You'll get a probability of 10 errors > per year. Maybe good enough for a Windows box but not acceptable > for your server. So you put in ECC to bring this probability back > into reasonable numbers. ECC can correct the single bit errors. > You only have to deal with double bit errors. Chance for them is > much much lower. > Yes, ECC, unlike parity, is a technique for reducing the error rate, with the side benefit of intercepting an error when it happens. I am not disagreeing with Larry that integrity checks are a Good Thing[TM], and in general are a hallmark of good engineering. However, they are not a replacement for ECC for the purpose of driving the failure rate down into an acceptable probability range. It is of course a very nice thing that DRAM prices have come down into the range where buying them in gigabyte quantities are reasonable :) -hpa -- at work, in private! "Unix gives you enough rope to shoot yourself in the foot." http://www.zytor.com/~hpa/puzzle.txt