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Parity / Non-Parity

Posted on 1998-12-01
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Last Modified: 2010-04-27
Can anyone tell me if taking the parity chip off of a 72pin DIMM will make it non-parity?

If you can convince me either way (preperably with supporting references)then I will give the points.

I am going to be hard to convince, without references on the web.
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Question by:reiters
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by:rosefire
ID: 1130130
The answer is yes, you can remove those chips to change the SIMM into a non-parity SIMM.


If you go to:

http://www.usa.samsungsemi.com/products/browse/dramsimm.htm

You will find that the DRAM presence detect bits are the same for the parity vs non-parity SIMM.  

The only problem I can see is you must be certain that you have correctly identified the parity bits so you remove the correct chips.  

To help you with this, find the memory at that site and look at the specs for the SIMM.
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by:jhance
ID: 1130131
My question is, why would you want to do this?  If it's really PARITY RAM then it will work in systems that take PARITY or NON-PARITY.  The NON-PARITY systems ignore the parity data so whether it's there or not doesn't matter.  

If you remove the parity chips (and it's not always just one chip), you run the risk of damaging the whole module.
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by:rosefire
ID: 1130132
That is a good question.  I noticed that I responded for SIMMs.  DIMMs should be the same.  I am checking on that now.  The bus memory width might be stored in the EEPROM but I can't see why it would be.  I'll get back to you on this.
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by:rosefire
ID: 1130133
OK, the answer is that you can remove the parity chips, but jhance is correct in saying that there should be no real conditions where you would want to risk ruining a module to make it non-parity.  If your application calls for a non-parity DIMM just use the parity DIMM.
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by:reiters
ID: 1130134
I just need supporting info that you can use parity in NPs place.

all my 4MB DIMMs are parity and I need memory for an HP printer in NP.  all the chips are layed out like:

|||| [] ||||

four regular chips, a small square chip, and four more regular chips.  I need to know if removing the small square chip will do it or just use it like it is.

First satifactory comment can be changed to answer for points.
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by:rosefire
ID: 1130135
It occured to me that one reason you might want to do this is to make use of a DIMM with a bad parity chip by converting it to a non-parity one.  So I can think of a reason to want to do this.  I would love to know what your reason is.
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by:rosefire
ID: 1130136
Here is a good reference on the presence detect that would be used to identify your DIMM.  The EEPROM contains no information on the SIMM width.  This documentation is from IBM.

http://www.chips.ibm.com/products/memory/serpdapp/serpdapp.html




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rosefire earned 100 total points
ID: 1130137
Oh, why didn't you say this was for an HP product!  Yes, you can subsitute a parity DIMM in an HP printer calling for a non-parity one.  I am an Electrical Engineer that designs these products at HP.  It isn't likely you will find a specific reference saying it is OK to make the substitutions of parity where non-parity is called for.  There are just too many DIMM manufacturers to list all possible SIMMs.  We assume the user will buy the cheaper non-parity DIMM. The reason is that most people wouldn't want to spend the money.  The parity bits in the SIMM or DIMM are usually not connected to anything on the main PCA (I say usually because someone might connect the outputs to a light pull up or down resistor to keep them from flying around, but I doubt it).  If you want to be convinced of this, take a volt meter and look at the resistance to ground (chassis ground should work) on the parity pins compared to the pins that are actually used in the printer. You will find that they are different.

keiths@sdd.hp.com




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by:reiters
ID: 1130138
You've convinced me...and that ain't easy.
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