From: swesterback@tnclus.tele.nokia.fi (Sten Westerback, Nokia Telecommunications, FINLAND)
Subject: Re: Memory parity error (Was:Video driver problem (I think))
Organization: Nokia Telecommunications.
Date: Tue, 5 Jan 1993 10:51:47 GMT

In article <199301042026.AA28630@yfn.ysu.edu>,         Rob Bakos <ad749@YFN.YSU.EDU> writes:
>>
>>In a posting DAJ@ABS.NLC-BNC.CA writes :
>>>
>>>
>>> On Jan. 1 (tired of football already) I added 4MB of RAM to my home system.
>>> This brought me up to 8MB total. 486@33MHz, Windows 3.1, ATI WonderXL (1MB)
>>> video, Seagate 210 MB HDD, NEC 3FGx monitor.
>>>
>>> The new RAM is exactly the same as the old, same speed, same 3-chip/SIMM,
>>> even same manufacturer.
>>>
>>> Close up the case, fire up the computer, run the CMOS setup to get the new
>>> memory info registered, even run QA Plus through 1 cycle of memory testing
>>> to make sure everything is OK. Checks out OK.
>>>
>>> Start Windows. System locks in the middle of initializing the Program Manager
>>> screen. Hard Boot: get the Program Manager screen, but as soon as I touch the
>>> mouse, I get a blank screen -- SYSTEM ERROR, Parity error...."
>>>
>>> Interesting! I reboot and this time I run QA Plus on the memory for over 2
>>> etc ... stuff deleted
>>>
>>> Thanks in advance
>>>
>>> *----------------------------------------------------------------------*
>>> |     Darryl Johnson                 Internet: DAJ@ABS.NLC-BNC.CA      |
>>> |     Programmer/Analyst             Voice:    (819) 994-6846          |
>>> |     National Library of Canada     FAX:      (819) 953-0291          |
>>> |  ** Personal, not National Library, opinions in ALL cases.... **     |
>>> *----------------------------------------------------------------------*
>>>
>>>
>>Darryl,
>>Several sources told me that the 3 chips type ram modules occasionally
>>cause malfunction problems in fast machines, even if they are 70ns or
>>less. There seems to be no valid explanation why but it is said that the
>>parity implementation in this type of chips is the cause of the trouble.
>>This problem never seems to show with the 9 chips ram modules.
>>I have seen the experiment of transferring 8Mb ram from a 386DX33 to a
>>486DX33 the 386 working perfectly well and the 486 even refused to boot!
>>removing 4meg & testing the remaining 4Meg showed 1 module to be 'defective'.
>>Putting all memory back in the 386 re-generated a perfectly working machine
>>with no errors. Frustrating but true, try to interchange the ram modules and
>>find out which one is generating the trouble.
>>Good luck !
>>
> 
> Before you try that, go to your CMOS setup and turn off parity checking.
> I had the _exact_ same problem, and it seemed to cure it all.
> 

I would'nt do that, even if my BIOS would allow it. The parity check is there
for a purpose and diabling it may lead to system integrity problems. This will
cause most problems in environments like Windows (3.1 or NT) that frequently 
uses all parts of the memory. 
 The best thing to do is to try to get the 3 chip ones exchanged. The problem 
obviously is caused by different signal timings in the 2 bit chip (parity) 
than in the two 4 bit chips (8 bit data).

So go on exchanging the modules, eighter to the place you bought them or else
sell them to a friend who need more memory (everyone does!).

Sten
BTW. I don't think any of the programs does check the parity bit. Probably
they even disable the parity error interrupt (NMI, even if it is externally
maskable!).
============================================================================
Sten Westerback (BSc. electronics)          Telephone: +358+0 +5115891(work)
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   Note that i am working, but not speaking for Nokia Telecommunications!
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