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Quad-Channel RAM: Is it Worth It?

2K views 2 replies 2 participants last post by  Jennifer Law 
#1 ·
In process of building a server. I read somewhere that you needed to populate all available RAM slots of a motherboard in order to get quad channel, so after reading that, and since I only need 32 Gbytes, I selected a motherboard that had only 8 (DDR3) RAM slots, planning on purchasing 8 X 4 Gbytes of DDR3 RAM for a total of 32 Gbytes, hopefully running as quad-channel.

However, the motherboard I selected is now out-of-stock, and the only acceptable alternative I find has 16 slots, so I would like to confirm this notion that all of the slots must be populated in order to get quad-channel speed. This would mean I would have to purchase 16 X 2 Gbyte RAM sticks, in order to get 32 Gbytes, which seems ridiculous to me. Actually, the whole idea of fully-populating a 16 slot board seems a little whacky.

Can someone clarify this for me? Here's the new motherboard I intend to use:

ASUS Z9PE-D16/2L SSI EEB Server Motherboard - Newegg.com
 
#2 · (Edited)
All memory slots do not need to be filled in order to enable quad channel operation.

The board you have selected is a dually. You may install either one or two CPUs. Each CPU has its own memory bank (see how they are grouped). Install DIMMs only in the slots for the installed CPU.

Re quad channel operation. No need to fill all slots, though you may if you wish. Probably your best bet, both in performance and economy, would be a 4 x 8GB package installed in like colour slots (blue or black). If desired at a later date, you could install a second 4 x 8GB set in the other four slots.
 
#3 ·
Thanks gcavan, for the detailed answer. It provoked me to wonder if it were possible for a 2 x 8 pair of RAM to run in quad channel and according to wiki the answer is no.

https://en.wikipedia.org/wiki/Multi-channel_memory_architecture

The architecture can only be used when all four, or a multiple of four, memory modules are identical in capacity and speed, and are placed in quad-channel slots. When two memory modules are installed, the architecture will operate in dual-channel architecture mode. When three memory modules are installed, the architecture will operate in triple-channel architecture mode.
So, in order to derive the benefit of quad-channel operation, I am going to need to populate each CPU with a multiple of 4 RAM sticks. Given a 32 Gbyte spec, and using two CPU's, that means I'll need 2 (4 X 4) kits of DDR3 (1600) RAM to achieve quad-channel on both CPU's.

So then my question is if there is a negative to doing 2 (4 sticks X 4 Gbyte) and getting quad-channel, vs. 2 (2 sticks X 8 Gbyte) and only getting dual channel. Again, the idea of backsliding into lower-tech 4 Gbyte sticks seems counter-intuitive to me, when 8 Gbyte sticks are available, and probably cheaper.

Is there a compelling reason to go one way or the other?
 
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