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From: zazula@uazhe0.physics.arizona.edu (RALPH ZAZULA)
Newsgroups: comp.sys.next
Subject: Re: Spotted Workspace ? Why? (and BlastApp??)
Keywords: memory errors, non-parity memory, spotted display
Message-ID: <1991Apr6.152816.502@arizona.edu>
Date: 6 Apr 91 21:13:22 GMT
Article-I.D.: arizona.1991Apr6.152816.502
References: <1991Apr3.230504.27819@mp.cs.niu.edu> <1991Apr5.075135.23325@cs.ubc.ca> 
 <1991Apr6.043551.29580@mp.cs.niu.edu> <1991Apr6.205555.21974@cbnewse.att.com>
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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.
>| >After all, it is the screen that's being affected.  But I'm no
>| >expert, only guessing like everyone else.
>| 
>|      Good point.  I wasn't thinking.  So, the VRAM is non-parity crap,
>| too, huh?  What a bummer.  Is the VRAM on a 68040 board like that, too?
>| I hope not because I just bought the upgrade kit a week ago (it's not
>| installed yet) and it will definitely ruin my day to discover that I'm
>| still going to have a toy computer instead of a real, production one.
>| >
>	What a load of s..t!  Do you really believe that you have a toy
>	computer just because it doesn't have parity VRAM?  How many parity
>	erros have you seen recently in "production" systems that cause all
>	your work to get lost when the system decided that it could no longer
>	continue?  Parity RAM does nothing to a system unless it contains some
>	ECC logic to correct the problem.  Parity RAM only informs the system
>	that some memory has gone bad.  Would you like your NeXT to shutdown
>	because you have a fault in you VRAM?  I certainly would not!!!!!

Hmm...  What happens when the parity bit goes in your parity memory?
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
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
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
one expects will happen to only 8-out-of-9 bits leaving parity in tact.
If you are really parinoid about memory going bad, then you should be looking
into more fault-tolerant systems.  

I've also been somewhat amused to see people talking about "random cosmics"
trashing bits...  I'd be more afraid of "random criminals" or "random
power spikes" etc...  Note, however, that I haven't done the calculation
for the cross-section of a cosmic (say, muon) with the 12Meg in my cube.
I guess I'd need to know the geometry of the RAM and how much added charge
is required to change a bit...  

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
> 
>| 
>|                                   Scott Bennett, Comm. ASMELG, CFIAG
>|                                   Systems Programming
>|                                   Northern Illinois University
>|                                   DeKalb, Illinois 60115
> 
>/*
>** ============================================================================
>**
>**  Felix A. Lugo
>**
>**	E-Mail (including NeXTMail):
>**			Felix_A_Lugo@ATT.COM
>**			att!ihcoco!coco
>**
>** ============================================================================
>*/

   |----------------------------------------------------------------------|
   | 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    |
   |----------------------------------------------------------------------|