Supermicro Dual Socket Memory Population

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hippyhappo

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Oct 3, 2016
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I have a Supermicro X9DRi-F dual socket motherboard that I'm purchasing memory for. I'm looking to populate all 16 memory slots with 16GB RDIMMs. My question is regarding memory speed. I'm using v2 Xeon processors, which support up to 1866MHz. However, looking at the memory chart for my motherboard (below), am I understanding it correctly that if all 16 memory slots are populated, dual rank memory rated at 1866MHz will only run at 1600MHz? In other words, is there basically no point in purchasing 1866MHz memory if I plan to populate all memory slots?

Thanks

 

Evan

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Jan 6, 2016
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Yep and also take note note that those speeds you seem to be looking at are for 1.5v DDR3, I tend to see at higher dimm sizes and newer/faster more often than not the low power 1.35v ram.

Having said all this you won’t notice that much difference between even 1600 and 1333 for example, unless your extreme memory speed sensitive apps, in almost every instance in general computer more slight slower memory is better than less slightly faster memory.
 
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hippyhappo

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Oct 3, 2016
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Yep and also take note note that those speeds you seem to be looking at are for 1.5v DDR3, I tend to see at higher dimm sizes and newer/faster more often than not the low power 1.35v ram.

Having said all this you won’t notice that much difference between even 1600 and 1333 for example, unless your extreme memory speed sensitive apps, in almost every instance in general computer more slight slower memory is better than less slightly faster memory.
Awesome, thanks for the info.
 

Evan

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Jan 6, 2016
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Awesome, thanks for the info.
And apologies for that info being full of typo’s !

How this memory speed stuff works I am not 100% sure, it has to be not just a cpu or generation thing.
Example;
- HPE gen8 using 2Rx4 low voltage rdimm the 2nd bank (8 dimm per cpu) still runs 100% or rated speed of what the CPU supports
- HPE gen8 populating the 3rd bank causes a decrease in speed
- HPE gen8 using LRDIMM takes the load off the memory controller and allows a consistent speed especially using the 3rd bank.

- then SM as you have indicated see’s the speed drop already using the 2nd bank

Anybody know why this is ? Just design and better tolerances with extended certification checks ?
 

hippyhappo

Member
Oct 3, 2016
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And apologies for that info being full of typo’s !

How this memory speed stuff works I am not 100% sure, it has to be not just a cpu or generation thing.
Example;
- HPE gen8 using 2Rx4 low voltage rdimm the 2nd bank (8 dimm per cpu) still runs 100% or rated speed of what the CPU supports
- HPE gen8 populating the 3rd bank causes a decrease in speed
- HPE gen8 using LRDIMM takes the load off the memory controller and allows a consistent speed especially using the 3rd bank.

- then SM as you have indicated see’s the speed drop already using the 2nd bank

Anybody know why this is ? Just design and better tolerances with extended certification checks ?
Yeah, I'd actually be pretty interested to know how this all works as well. I did come across this Lenovo x240 which uses Xeon V2 processors, with 384GB of 1866MHz dual rank memory (all 24 memory slots populated):

IBM Flex System x240 2 x E5-2690V2 3.0GHz 384G 10GbE NIC 16G FC 8737 AC1 TOP | eBay

He has a screenshot of the BIOS and it's running at 1333MHz @ 1.5v (which is faster than the speed specified in the Supermicro chart for such a configuration), so it must (at least in part) have something to do with the motherboard.

Kind of makes me wonder why they sell registered DIMMs at some of these voltage / speed combinations, when they don't run at the advertised speed in the configurations they're typically used in.
 
Last edited:

hippyhappo

Member
Oct 3, 2016
37
7
8
34
And apologies for that info being full of typo’s !

How this memory speed stuff works I am not 100% sure, it has to be not just a cpu or generation thing.
Example;
- HPE gen8 using 2Rx4 low voltage rdimm the 2nd bank (8 dimm per cpu) still runs 100% or rated speed of what the CPU supports
- HPE gen8 populating the 3rd bank causes a decrease in speed
- HPE gen8 using LRDIMM takes the load off the memory controller and allows a consistent speed especially using the 3rd bank.

- then SM as you have indicated see’s the speed drop already using the 2nd bank

Anybody know why this is ? Just design and better tolerances with extended certification checks ?
I've been doing some searching and came across this on Supermicro's website:

https://www.supermicro.com/support/resources/memory/X9_DP_memory_config.pdf

On the bottom there is a FAQ and one of the questions is the following:

Question:
I am using one of your 16DIMM Dual Processor motherboard with E5-2600 v2 processors and I’d like to use LVRDIMM (1.35V) memory running at 1600MHz,but the system BIOS keeps setting the speed to 1333MHz. Why won’t it let me run the DIMMs at full speed?

Answer:
LV-RDIMM is running to Intel specifications at 1333MHz (see Socket R memory table) for a 1.35v device. It is possible to run the LVDIMMs at 1600MHz by going into the BIOS and choosing FORCE DDR3 1600. This is still technically within the memory vendor’s spec, but it needs to be done manually because of the 1.35V characteristics of the LVDIMM.

So it sounds like Supermicro is just abiding by the official Intel spec by default, but gives you the option to override it manually. It sounds like the other manufacturers simply set their defaults outside the official Intel spec.