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Old May 17, 2013, 10:25 AM   #1
-PM-
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Join Date: May 2013
2008 Mac Pro - Why do 2GB sticks of server FB-DIMM RAM work but 4GB sticks do not?

Hey guys, new to the board, but long time follower. I have a question that has been bothering me for almost a year.
I have been able to install 2GB sticks (up to 8 for a total of 16GB) of PC2-6400F from random servers (HP, IBM, etc.) in a 2008 Mac Pro without a single issue.
But when I try to use 4GB sticks (also from random HP or IBM servers) of PC2-6400F, they are never recognized. All 4 of the red lights are on for each of the modules and the power LED blinks. No startup at all.
I have tried every memory configuration possible with no results. I have tried over a dozen different working pairs of matching 4GB sticks on 4 different 2008 Mac Pro's without any success.
Can anyone shed some light on this matter? I have searched and searched, but couldn't find anyone that has an issue like mine.
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Old May 17, 2013, 10:55 AM   #2
xcodeSyn
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Join Date: Nov 2012
Quote:
Originally Posted by -PM- View Post
But when I try to use 4GB sticks (also from random HP or IBM servers) of PC2-6400F, they are never recognized. All 4 of the red lights are on for each of the modules and the power LED blinks. No startup at all.
...
Can anyone shed some light on this matter? I have searched and searched, but couldn't find anyone that has an issue like mine.
The answer to your question is right in this post, any quad rank (4R) FB-DIMM modules won't work with the MP, but dual rank (2R) will. You should read the whole thread to see your options.
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Old May 17, 2013, 11:11 AM   #3
-PM-
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Thanks. That's exactly what I was looking for. Can't believe I missed that detail throughout my searches.
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