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From: rwallace@vax1.tcd.ie
Newsgroups: comp.arch
Subject: Re: Workstation Data Integrity
Message-ID: <6816.26df0567@vax1.tcd.ie>
Date: 1 Sep 90 00:48:39 GMT
References: <1990Aug3.204358.330@portia.Stanford.EDU> <40694@mips.mips.COM> <2399@crdos1.crd.ge.COM> <1990Aug10.171744.9639@zoo.toronto.edu> <2421@crdos1.crd.ge.COM> <1990Aug18.210132.25203@sco.COM> <2434@crdos1.crd.ge.COM> <6797.26d6edce@vax1.tcd.ie> Lines: 37
Followup-To: 9@crdos1.crd.ge.com>
Lines: 38

Organization: Computer Laboratory, Trinity College Dublin
Lines: 34

In article <2469@crdos1.crd.ge.COM>, davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) writes:
> In article <6797.26d6edce@vax1.tcd.ie> rwallace@vax1.tcd.ie writes:
> |                                           OK take the very unlikely case that
> | it is in your data. For me that means in the source for a program I'm writing.
> | This is no problem, I can just fix the one trashed character when the compiler
> | barfs on the code. 
> 
>   One bit changes 0 to 1, + to *, etc. Your compiler catches this?
> 
> |                    Much better than having the machine crash and lose several
> | minutes' work. Or say the error is in a floating-point number in a spreadsheet.
> | Chances are the program will crash with a floating-point error or at least
> | produce obviously wrong results e.g. profit for 1989 was $-32198742.88888.
> | 
> | The point is that ignoring a parity error is a pretty safe thing to do; there's
> | very little chance of getting a misleading answer.
> 
>   A little though should show you the error of that thought. Over half
> the word is dedicated to less significant bits of the mantissa. An error
> in any of those bits will result in a percent or less change.

OK fair point, and other people have pointed out that parity is only checked
when reading/writing an individual memory word. I still think it would be MUCH
more useful for the operating system to flash up a message telling you that a
parity error had been detected and where it was, so I could decide for myself
whether to reset the machine. (A likely response if doing stuff with very
important data is to save your work under a different filename and then compare
your modified version with the previous version to check if there are any
differences other than in the section you modified).

"To summarize the summary of the summary: people are a problem"
Russell Wallace, Trinity College, Dublin
rwallace@vax1.tcd.ie

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