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TR3XG1600C8DG mem limit and I7


rickhan

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I have a new ASUS P6X58D Premium motherboard.

The manual says "Due to Intel spec, DDR3 1600 mem are supported for one DIMM per channel only."

What does this mean?

I have the 6GB kit now, and I plan to add another 6GB kit later.

Is that not possible with this memory?

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The memory should run at 1600MHz in the 6GB kit however it is considered overclocking. As far as running 12GB of memory you may need to slow it down to 1333MHz in order to run. It all really depends on the memory controller in the CPU however.
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I have a new ASUS P6X58D Premium motherboard.

The manual says "Due to Intel spec, DDR3 1600 mem are supported for one DIMM per channel only."

What does this mean?

I have the 6GB kit now, and I plan to add another 6GB kit later.

Is that not possible with this memory?

 

Officially, it means that you should not run memory any faster than 1333MHz (DDR3-1333) if you are using two kits. The limitation is not only Intel spec, it's a JEDEC recommendation as well. This is because at present all 2GB and 4GB modules are double-ranked. It should have been worded "Due to official JEDEC spec, DDR3 1600 mem are supported for two ranks (two single-rank DIMMs or one double-rank DIMM) per channel max." Using two 6GB or 12GB kits would result in four ranks of memory per channel. You can try running the full 1600MHz speed with two kits, but operation may not be guaranteed stable.

 

Anyway, the limitation is a moot point considering that a stock i7-920 officially supports only DDR3-1066 memory (or more specifically, memory operation at DDR3-800 or DDR3-1066 speed). On some motherboards, you may have to overclock your CPU in order to run memory any faster than 1066MHz. On other motherboards (particularly those whose BIOS supports Intel-certified XMP settings), you can select the XMP 1600 profile in the BIOS' memory configuration menu with the processor still at stock speed to run one kit at 1600MHz. This will set the FSB:DRAM ratio to 2:12, the DIMM voltage to 1.65V or a setting nearest to it and the VTT (QPI/Uncore voltage) to 1.35V (the latter two voltage figures are the Intel-recommended maximums for the i7). In other words, running the i7-920's memory controller any faster than the official DDR3-1066 maximum is considered overclocking. This is a limitation shared by all other current non-i7 Extreme Socket 1366 processors.

 

Oh, I see that the RAM GUY had already responded with the DDR3 1333 part.

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If I want to run 12, then I would need to buy faster memory?

 

No. It's just that all memory controllers will default to a lower speed when more than one double-ranked module per channel is installed (the maximum recommended or forced speed limit). In fact, I would not recommend buying faster memory because the CPU's on-package memory controller simply could not keep up with the speed increase, and thus would have dropped the speed to well below the rated speed anyway. The Intel memory controller is not truly on the CPU die but is actually on a separate circuit board that's connected to the main CPU die underneath the same heat spreader. Thus, it is an "on-processor-package" controller, not an "on-die" controller like the AMD processors have. Even if you get ultra-fast memory, you'll still need to lower the memory speed to 1333 with all six slots filled in order to get things stable. And actually, with a Socket 1366 platform, even 1333 is considered overclocking. That platform does not officially support memory speeds faster than 1066.

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  • 3 months later...

Great, Great, Great explanation! I've been Googling my **** off finding such simple/clear explanation. So thanks! :-)

 

So I basically have 2 options:

1. Run my 12GB RAM (CMP6GX3M3A1600C7 x 2) @ 1333Mhz or

2. Use XMP and OC @ 1600Mhz and find out if it runs stable?

 

Now, I do have an additional question about this, almost in every text I come across about this issue the following (exact) statement arises: "Due to Intel Spec Definition, X.M.P. Dimms and DDR3-1600 are supported for one Dimm per channel only." and I can't help myself wondering why this doesn't state "1600 or higher", I always read 1600Mhz specifically. Is there a specific reason for this? I would still be having the same problem if I had 1866Mhz memory, right?

 

RAM used to be the easy part of a system :laughing:.

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