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From: bennett@mp.cs.niu.edu (Scott Bennett)
Newsgroups: comp.sys.next
Subject: Re: Spotted Workspace ? Why? (and BlastApp??)
Keywords: memory errors, non-parity memory, spotted display
Message-ID: <1991Apr8.021158.17858@mp.cs.niu.edu>
Date: 8 Apr 91 02:11:58 GMT
References: <1991Apr6.043551.29580@mp.cs.niu.edu> <1991Apr6.205555.21974@cbnewse.att.com> <1991Apr6.152816.502@arizona.edu>
Distribution: world,local
Organization: Northern Illinois University
Lines: 88

In article <1991Apr6.152816.502@arizona.edu> zazula@uazhe0.physics.arizona.edu writes:
>In article <1991Apr6.205555.21974@cbnewse.att.com>, tyc@cbnewse.att.com (felix.a.lugo) writes...
>>In article <1991Apr6.043551.29580@mp.cs.niu.edu> bennett@mp.cs.niu.edu (Scott Bennett) writes:
>>| In article <1991Apr5.075135.23325@cs.ubc.ca> sritchie@cs.ubc.ca (Stuart Ritchie) writes:
>>| >In article <1991Apr3.230504.27819@mp.cs.niu.edu> bennett@mp.cs.niu.edu (Scott Bennett) writes:
>>| >>In article <5596@media-lab.MEDIA.MIT.EDU> simsong@daily-bugle.media.mit.edu (Simson L. Garfinkel) writes:
>>| >If software still runs, it sounds to me like the VRAM is shot.
>>| >  [text deleted  --SJB]
>
>Hmm...  What happens when the parity bit goes in your parity memory?

     The same thing as with any of the other bits.  You get a single-bit
error.

>With the odds being 1-in-9 (if you really believe that bits bite the dust
>quite often) I can't see parity memory as something to put ones mind at
>ease...  I also agree that the video memory isn't as critical as program/data

     Most parity, non-ECC memory is not up to detecting errors of two
or more bits in a byte.  However, most errors are single-bit errors
because only one chip is going bad, and memory that's going bad will
be likely to have single-bit errors before it starts getting multiple-bit
errors.  Then you can get it replaced.

>RAM.  An acceptable thing would be for the system to report bad VRAM at
>power-up.  As for program/data RAM, there are a lot of 8-bit MAC's out there

     I disagree.  As you know by now, many errors are intermittent,
especially when they first crop up.  A chip going bad might not make 
the error, for example, when you first turn the machine on and the
chip is still cool.  Give it ten or fifteen minutes and it may have
problems.

>being used for many things.  I don't see a lot of people complaining about
>loss of data or poor results (eg. FermiLab, Argonne...).  I don't know what

     Well, maybe for word processing it isn't that important.  If they're
using it for anything more sensitive, well, ignorance is bliss, at least
for a while...  Besides, if the hardware can't tell them, how would
they even know?

>one expects will happen to only 8-out-of-9 bits leaving parity in tact.

     Well, that would be a multiple-bit (i.e. multiple chip) error.
Not much you can do about that, beyond maybe detecting a double-bit 
error, but that does take considerably more costly equipment.

>If you are really parinoid about memory going bad, then you should be looking
>into more fault-tolerant systems.  

     Like pee cee clones, maybe?  As overrated as they are in most
other ways, pee cees and their clones can usually at least tell you
when they've f****d up.
>
>  [text deleted  --SJB]
>
>If you disagree with any of this, it may not be what I typed... Could
>have been a 1GeV u kicking through this document...

     :-)
>
>:-)  
>
>Ralph
>> 
>
>   |----------------------------------------------------------------------|
>   | Ralph Zazula                               "Computer Addict!"        |
>   | University of Arizona                 ---  Department of Physics     |
>   |   UAZHEP::ZAZULA                            (DecNet/HEPNet)          |
>   |   zazula@uazhe0.physics.arizona.edu         (Internet)               |
>   |----------------------------------------------------------------------|
>   |   "You can twist perceptions, reality won't budge."  - Neil Peart    |
>   |----------------------------------------------------------------------|


                                  Scott Bennett, Comm. ASMELG, CFIAG
                                  Systems Programming
                                  Northern Illinois University
                                  DeKalb, Illinois 60115
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