Messages in this thread |  | | From | (H. Peter Anvin) | Subject | Re: Wow! Is memory ever cheap! | Date | 10 May 2001 15:44:10 -0700 |
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Followup to: <3AF9B0D2.F2E330F9@gmx.de> By author: Edgar Toernig <froese@gmx.de> 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 :)
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