Computer Flake Outs (was: Re: On Overclocking - READ THIS!)

Rodney R. Korte (
Tue, 06 May 97 23:58:47 -0400

On Tue, 6 May 1997 22:57:55 -0400, Nelson Minar wrote:


>The big question is whether those errors will be significant to the
>computation. It is worth thinking about what random failures mean to a
>huge computation like deschall. Other parts of computers flake out:
>memories fail (especially if you don't have parity or ECC), a register
>could get hit by a cosmic ray, etc. Anyone care to estimate the number
>of random bit errors that will occur over 2000 years of PPro 200

Now this is the most interesting thing that's come up in this list
in a while, IMO! I think the point about memory errors is the most
interesting. I don't care to start a whole non-parity vs. parity.
vs. ECC memory debate, but there used to be a very interesting
article at (it's not
there anymore, don't know where it is) called "Parity Questions
Answered" that gave some numbers with regards to memory errors.

It claimed something like one one-bit error every 4-6 months for
the average Pentium-class computer with 32MB, or something similar
(I wish I could find that document again- perhaps someone can solidify
these numbers). The chance of a multiple-bit error was several
orders of magnitude less.

Let's make a really rough estimate based on this:

The memory footprint of DESCHAL5 on my machine is about 1/2 MB,
so I could expect an error in memory in which the DESCHAL code
resides about once in 3 years. Admittedly, by probability skills
are next to nil, and this may prove it, but supposing that there
are currently 2000 Intel machines searching key blocks, there
should be a one-bit memory error in one of these machines within
the DESCHAL code every day or even more frequently, correct?

Fortunately, I have parity memory, which will catch a one-bit
error, and thus not cause a problem for the DESCHAL effort.
However, I'd guess that a large percentage of the Intel machines
running DESCHAL have non-parity memory, and wouldn't be able to
catch such errors.

Well, this all seems scary, but the chance of having a critical
memory error in a client that is crunching the key block with
the one and only true key, and that client reporting back "Key
not found" must be *extremely* tiny.

Probably smaller than the chance of a malicious attack. ;-)


Rodney R. Korte                   OS/2. Operate at a higher level.    ---> MIME, PGP (finger for key) welcome.

Crack DES NOW!