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bniu

macrumors 65816
Original poster
Mar 21, 2010
1,120
303
i read somewhere that it is preferable for the Mac Pro to have memory installed with either 3 or 6 modules for a total RAM amount in multiples of three. Why is this that the Mac Pro works best in multiples of 3 (i.e. 3, 6, 12, 24, 48, 96)? I thought RAM is usually ideally configured in powers of 2 (2,4,8,16,32,64).
 

CaptainChunk

macrumors 68020
Apr 16, 2008
2,142
6
Phoenix, AZ
i read somewhere that it is preferable for the Mac Pro to have memory installed with either 3 or 6 modules for a total RAM amount in multiples of three. Why is this that the Mac Pro works best in multiples of 3 (i.e. 3, 6, 12, 24, 48, 96)? I thought RAM is usually ideally configured in powers of 2 (2,4,8,16,32,64).

This is because the Nehalem/Woodcrest (2009/2010) Mac Pros use a triple-channel memory controller. Thus, sets of 3 is ideal. But the performance difference when installing RAM in dual-channel configuration is generally negligible for most uses.

Oddly, the 2009/2010 Mac Pros have 4 or 8 slots (depending on whether it's SP or DP, respectively). But the base RAM configurations are 3 or 6GB, installed in tri-channel configuration. They really should equip the machines with 6 or 12 slots, but for whatever reason (maybe space concerns), they don't.

I wouldn't totally worry about triple channel if you prefer more RAM and want to fill all the slots. For example, newer versions of After Effects will prefer a 16GB machine in dual-channel configuration versus a 12GB machine in tri-channel.
 
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