Mac Pro (mid 2010) 8-core memory slots not recognized

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Mac Pro (mid 2010) 8-core memory slots not recognized

Hi, I've run out of ideas and was hoping someone could help me. I have a Mac Pro (mid 2010) 8-core with the basic 6 x 1gb memory dimms. I just inserted two new 4gb dimms in slots 1&5, and moved the existing 1gb dimms to slots 4&8. There is no problem with the new memory but I can't get the computer to recognize the full eight slots. I have tried with just six slots and it sees everything but when I fill all eight it stops recognizing slots 3&4. I've tried restarting with option, command p & r held down, and I've taken all the cards out and rearranged them several times but get nothing different. Any other ideas?

many thanks

Em

Mac Pro, iOS 8.3, 8-core 2010

Posted on May 15, 2015 6:31 AM

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Answer 1

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Grant Bennet-Alder

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May 15, 2015 1:03 PM in response to Emmiephoto

There are three memory channels on each side of the processor board on the 2009 through 2012 Mac Pro with two processor chips. Each side operates independently. Slots 3 & 4 and slots 7 & 8 are shared with each other. Depending on how your DIMMs are constructed, they may not end up "playing nice" when used in the "shared" slots.

More specifically, DIMMs constructed with too many ranks of chips will not be able to operate properly in the "shared" slots because there will be too much bus loading with TWO such DIMMs in the "shared" slots. These may very well be genuine Apple DIMMs. That does not change anything.

This is different from another problem encountered with larger DIMMs in these Macs. Some larger DIMMs have so many Ranks of chips that they would not be able to run at all -- so many ranks of chips cause too much Bus Loading all by themselves. In this case, a Register in added to the DIMM so that only the Register loads the Bus, not the many ranks of chips. These DIMMs are called "Registered" DIMMs and they do not play nice with regular DIMMs at all. But this is NOT the problem you are seeing.

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Answer 2

May 15, 2015 5:58 PM in response to Emmiephoto

It occurred to me that if you inspect your 6 1GB DIMMs carefully, you may find there are some with a different number of chips on the DIMM. These may behave differently from the ones you already tried in the last two "shared" slots.

If that is not an option, try with slot 4 and eight empty.

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Answer 3

Emmiephoto Author

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Jun 1, 2015 3:21 AM in response to Grant Bennet-Alder

Thank you Grant. I managed to get it to work with slots 4 & 8 empty. They all have the same number of chips so no combination allowed me to have the full memory at my disposal but everything is a lot faster now anyway!

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