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From: pnelson@hobbes.uucp (Phil Nelson)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Parity Checking / ECC RAM on the A3000
Summary: Parity checking can provide useful information
Message-ID: <3649@tymix.UUCP>
Date: 7 Jun 90 20:15:45 GMT
References: <756@bilver.UUCP> <1990May27.101258.24470@zorch.SF-Bay.ORG> <321@tlvx.UUCP> <1990May29.204550.27961@zorch.SF-Bay.ORG> <90151.123059LEEK@QUCDN.BITNET>
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In article <90151.123059LEEK@QUCDN.BITNET> LEEK@QUCDN.QueensU.CA writes:
|From the articles in the ECC/Parity bit thread that I have been reading so far,
|it seems to me that memory error is far less likely to be the cause of system
|realibility concern...  The realibility of a system is only as good as the
|weakest component.

 You may want to consider that what you have reading is the opinion of some
people that memory chips are so reliable that "parity is useless". The facts
(if we had any) may be otherwise. If the Amiga had parity, it would easy to
get good data on the reliability of the memory IN THE BOX (not in some chip
test lab) and IN THE FIELD (not some clean, quiet final test area).

|  I have seen my machine crashing more often due to programming bugs and bad
|programming.  How clean is the power source that we plug our trusty machine into
|?   Can we trust the power company to deliver 100% regulated power free of power
|surges and brown outs ?  (Answer is NO !!)  Can we trust the other appliances
|in the building for not producing power surges ?  That's the reason why some
|companies make a fortune selling UPS and power conditioner.

These are good points. I think it very likely that the memory system is not
the greatest cause of unreliability on the Amiga. Certainly not if you
include software bugs. This does not prove that parity checking is useless,
but that other measures are needed too. The order in which to take measures
to improve reliability is not determined exclusively by which is the worst
problem, it may be reasonable to start with a problem that is not the worst,
if a solution is easily implimented (memory parity checking, for example).

|  How much do we trust our CPU to not to fail ?  Is there some hidden bugs in
|the CPU or perpherial chips that would fail under some conditions ?
|
|Intel got a few of these nasty bugs in their early batches of 386 CPUs
|chips etc.. (I am sure things like this would pop up once in a while.) Some
|companies insists on running parts outside their specified range.  This might
|potentially cause problems when mixed with other out of spec designs.
|
|The list of things that can go wrong can go on forever.  My point is that the
|memory system is one of the less probable cause of system failure.  Given the
|cost of ECC, it might be more worth while to spend that money to prevent other
|more likely cause of failure...

 I think the cost of ECC cannot be justified on the Amiga, unless for special
applications. The added cost of simple parity checking (not very great) might
easily by justified because it would help by allowing the early detection
and repair of machines with memory problems. It would be especially useful
for machines with flaky, intermittent memory.


|K. C. Lee


Phil Nelson . uunet!pyramid!oliveb!tymix!hobbes!pnelson . Voice:408-922-7508

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