Strange behavior of 2008 Mac Pro - DIMM installation

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Strange behavior of 2008 Mac Pro - DIMM installation

I have a Mac Pro 3,1, running Mavericks, currently with 6GB of 800Mhz RAM, that I'm attempting to add four additional 1GB DIMMs to. The memory has been confirmed as working in both this and another, similar machine. The current setup has a 1GB DIMM in socket 1 and a 2 GB DIMM in socket 3 on both memory risers. If I attempt to add DIMMs to either the 2nd or 4th socket on either riser the memory is not recognized, and in fact can sometimes interfere with the memory installed in the first and third sockets. I've tried all sorts of permutations of both the new and old memory, I've tried both memory risers together and each individually, and consistently there is a problem with the even numbered sockets.

Anyone ever encounter this problem, or know that might cause it?

Mac Pro, OS X Mavericks (10.9.5)

Posted on Oct 3, 2014 8:47 AM

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Answer 1

The hatter

Level 9

60,990 points

Oct 3, 2014 9:04 AM in response to swechsler

That is not the arrangement called for by Apple.

DIMM sets are on t he same Riser using 1/2 and 3/4

Only when they were shipped or have only ONE pair can they properly be used with one on each Riser.

Sometimes due to PROBLEMS people resorted to try and use DIMMs in that manner.

I would not buy 1GB DIMMs. 2 x 2GB sets are cheap, $25, and ideal is to fill all DIMM slots.

16GB would be fine, and cost $100.

Mixing different types and mixing can pose trouble in some cases.

Higher density DIMMs normally should be in lower numbered slots on each Riser.

Mac Pro (Mid 2012 and earlier): How to remove or install memory

btw, 667MHz works just fine, often cheaper and easy to find ("Mac Pro FBDIMM DDR2 667" on Amazon)

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Answer 2

swechsler Author

Level 1

21 points

Oct 3, 2014 9:44 AM in response to The hatter

Thanks for your response, but it didn't really answer my question.

1: I already have the 1GB DIMMs, and don't want to purchase additional, expensive memory for such an old machine.

2: I tried both risers, fully populated, and had the same problem. I was only experimenting with filling different sockets to determine what the problem was. Currently the only sockets that work are 1 and 3.

Edit: the article that you linked to doesn't specify using specific socket numbers, only that they should be installed in pairs, on both risers.

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Answer 3

The hatter

Level 9

60,990 points

Oct 3, 2014 9:54 AM in response to swechsler

I said $25 for 4GB, how much cheaper can you go? one set would be all you need except for this:

http://www.amazon.com/2008-PC2-6400-Buffered-FB-DIMM-MA970LL/dp/B007GB1I7K/ref=s r_1_3?ie=UTF8&qid=1412355067&sr=8-3&keywords=mac+pro+fbdimm+800mhz

filling all 8 DIMMs = 17% improvement in memory performance.

Well take it from me: install in pairs on the same Riser in adjoining slots.

Someone was kind enough to create a chart.

Apple was kind enough to keep changing tech notes.

Your arrangement is totally not kosher.

The fact yours "work" is a sign actually that they DO NOT WORK as engineered.

For $8 more these kits of 4GB also work properly.

My Mac Pro is 2006 1,1 and 8 yrs old, works better now than ever, has 8 x 2GB plus 500GB SSD for system and 500GB for graphic libraries and ATI 5770. Yes I feed it and take care of it and it does all I ask of it.

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Answer 4

swechsler Author

Level 1

21 points

Oct 3, 2014 10:21 AM in response to The hatter

Those DIMMs are $34, not $25. And which arrangement are you talking about that's not good? I wrote in my OP that I experimented with all different sorts of arrangements, including 1GB DIMMs in sockets 1 and 2 of both risers, which also didn't work.

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Answer 5

notcloudy

Level 4

1,252 points

Oct 3, 2014 10:32 AM in response to swechsler

Did yours come with a Everything Mac manual -- I have mine - has very specific rules on installing memory - also what type and specifics.

Never needed above the 4GB I have with snow leopard -- and have not had an issue with it.

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