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Is it possible to install 24 GB RAM by using all 12 RAM slots (2GB sticks each) on a dual socket mainboard even though only 1 CPU is installed? (this is on a Dell R710).

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3 Answers 3

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The Dell R710 does not support this type of configuration - the DIMM banks are per CPU - with 9 DIMM slots per socket ( three DIMMs per channel, three channels per CPU) for a total of 18 DIMM slots. If you install DIMMs in the slots for the second CPU they cannot be accessed by the primary. More specific DIMM configuration details can be found here. For a single CPU system the maximum RAM is 96GB but you cannot use more than 9 DIMMS in total to get to that number. Just as a reminder, if you do fully populate all DIMM slots in a channel you are going to be limited to 800Mhz memory speed.

The Dell R810 has a slightly different architecture that Dell call FlexMem Bridge (described in this Anandtech Review) that does support populating all DIMM slots even when only one CPU is installed but that is a very different system.

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Got it. Please confirm that I'm right with the following then. I have Windows Server 2008 R2 Standard, which at most supports 32 GB RAM. When I get the first CPU, I should only get 12 GB (6x2) as the next higher configuration is 24 GB (6x4), which I can't duplicate when I get the second CPU (that would be 12x4, or 48GB total, which is 16GB more than supported by my Windows version). Correct? –  AX1 Dec 22 '10 at 17:37
    
You could configure 24GB now (6x4GB) then move 3 of the 4GB DIMMs when you add a second CPU and add a further 6x1GB. That would be the maximum that the system can support while staying under the 32GB limit and ensuring that all memory channels are balanced which you will need to do. The DIMM sizes in each channel don't need to matched within each set of three but all 3 (or 6 for dual CPU) channels should be configured the same way so you could start off with 15GB (3x4GB + 3x1GB) even though that looks strange and duplicate that with the second CPU. –  Helvick Dec 22 '10 at 17:54
    
Could I also do 9x2 GB (single), and 18x2 GB (dual)? It would be 36 GB of RAM but all equal DIMMs. Or is there a tradeoff from using all 9 slots per CPU? –  AX1 Dec 24 '10 at 6:17
    
You can but the memory speed is limited to 800Mhz with all 3 slots per channel occupied whereas with 2 you are likely to be able to run them at 1333Mhz (if your CPU is up to it, the RAM is 1333Mhz and not Quad Ranked). That is a noticeable difference but only relevant if you are configuring with a CPU that supports DIMM speeds faster than 800Mhz. –  Helvick Dec 24 '10 at 8:29

Yes. I have 2 in that configuration now.

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R710's? Single CPU with 12 DIMMs working? –  Helvick Dec 21 '10 at 21:06

Yes, the amount of RAM is completely unrelated to the number of CPUs.

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