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User profile for user: Mark Hannon
Mark Hannon Author
User level: Level 1
84 points

2nd pair of DIMMS suddenly unrecognized by Mac Pro 1.1

I purchased a pair of 667MHz for my Mac Pro 1.1 a few years ago. There were no problems until earlier this week my computer began to slow down. I checked the Activity monitor which showed a small sliver of free memory and then checked the System Profiler. The original pair of 512 DIMMs were listed but the 2nd pair of 2GB DIMMS were missing from the report.


I know for a fact that the DIMMS were installed because the panel was open and I had removed the trays and reseated the DIMM sticks before strating up again.


The only symptom of the DIMMs disappearing was the slowdown of my Mac Pro. I tried swapping the position of the pairs, purchased pair to the top tray, original pair to the bottom tray. This resulted in a startup error. I've switched the position back and it's working, albeit a bit slowly.


Clearly my extra DIMMs went bad so I've removed them and have another pair on order from OWC. But I am curious, is there a way to test memory that your computer can't see?

Mac Pro, Mac OS X (10.6.8), MP 1.1

Posted on Jan 26, 2013 12:19 PM

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5 replies
User profile for user: The hatter
The hatter
User level: Level 9
60,990 points

Jan 26, 2013 12:28 PM in response to Mark Hannon

How To Install and Remove Memory Mac Pro

https://support.apple.com/kb/HT4433


2x2GB FBDIMM DDR2 667MHz @ $35

http://www.amazon.com/BUFFERED-PC2-5300-FB-DIMM-APPLE-Memory/dp/B002ORUUAC/


Over time, heat kills, and the stress of heat cycles.


I have heard/seen people lately have to go through 2-3 sets from OWC to get it working.


I would not even bother with 512's.


You should have quad set with a pair on each Riser. So $70 Amazon 8GB set for instance.

Always try iwth just new RAM installed. AHT and Rember is half way decent way to test.


Run the fans @ 800 rpm instead helps too. And monitor that they do stay in 65*C or less - more than 70 is not good.


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User profile for user: Grant Bennet-Alder
Grant Bennet-Alder
User level: Level 10
127,141 points

Jan 26, 2013 12:52 PM in response to Mark Hannon

The answer to your query has been presented to you. There is no point in attempting to test memory your computer can't see. You already have all the information you need. That memory is Bad.


Mac Pro 65lb tower features Error Correcting Code RAM. Eight additional syndrome bits are stored with each 64-bit word in main store. When read back, each and every memory transaction is checked by Hardware in the Xeon processor. Single-bit errors are corrected on the fly. Uncorrectable errors, such as double-bit errors are intended to cause a kernel panic.


But if your Mac Pro detects that a section of RAM is already Bad at Startup, it is simply mapped out. That is what has happened to you. The Power-On Self Test determined it was bad, and WILL NOT use it.


Hardware sat there and checked each transaction. It was Bad -- too bad to be usable. Accept that you have bad RAM and move on.

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2nd pair of DIMMS suddenly unrecognized by Mac Pro 1.1

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