Memory bus speed with mixed 16GB & 8GB DIMMs???

[chuckk281]

Rick had a customer question rgarding DIMM memory speeds:

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A customer wants to configure 144GB memory in a 2P BL460G7 for VDI.  Is my answer below correct for the bus speed AND the requirement for X5600 series CPUs to run the new 16GB DIMM at 1333?

1)      If they use the new dual rank, 16GB DIMMs (627812-B21/$1,348 list ea) AND an X5600 series CPU, they will get the best memory performance (1333MHz bus speed.)

2)      If they use the older quad rank, 16GB DIMMs (500666-B21/$899 list ea), I THINK the memory bus will run at 800 MHz and their memory performance will be 40% slower.

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A couple of experts replied to Rick:

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Steve: 

Rick, yes, I believe 2x16 and 6x8 in dual ranked DIMMs should get you to 144GB at 1333Mhz.  144GB is not shown on the chart in the QS, but I don’t see why it would not. 

Also, the E5649 processor runs at 1333Mhz, so if they aren’t asking for the X-series CPU and just want 1333MHz and/or 6 cores, they can get both in the 80 watt E5649.

Dan also confirmed:

Steve is correct.  You can do (6 x 16GB DR) + (6 x 8GB DR), and this will yield 144GB of memory, running at 1333MHz.

Also correct about the E5649 processor (and the E5645 too) running memory at 1333.  Intel broke the former “rule” about needing an X-model 5600 series to run at 1333 when they launched these speedbump processors in February.

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Comments or suggestions??