Max Ram speed for Asus P9 X79 Pro?

SLP Firehawk

Weaksauce
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Jan 30, 2020
Messages
112
I currently have 64GB RAM in my P9X79 Pro system. It is 1600Mhz. What is the max Ram capacity and speed I can use? I think it's 64GB and 2400MHz but not sure. I want to get the best out of it that I can
EDIT: and if I am changing the 3930k CPU to a Xeon do I have to use ECC RAM?
 
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Grebuloner

Gawd
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Jul 31, 2009
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944
There are a lot of "it depends" answers here.

1) Capacity: If you are willing to spend the money, the max capacity (with last bios) is 128GB (8x16GB), but you have to use the very rare and probably very expensive I'M (Intelligent Memory) 16GB, 1600MHz modules. No one else made that capacity, and I can't even find any for sale on fleabay, right now.

2) Speed: 2400MHz is pretty high end for Sandy Bridge and not all chips can run it with stability, and there are even faster speeds out there if you want to spend the money for it. YMMV with an 8 year old chip. It gets even harder if you want to use 8 DIMMs. One of my 3930k's will run 4x8GB at 2400, the other can't, but does happily run 8x8GB at 1866.

3) Xeon stuff: This is where things get weird. You do not have to run ECC with a Xeon CPU. In fact, you can't, because it also requires that the motherboard is built for ECC support, and yours is not. ECC DIMMs might (might!) actually be recognized and used if installed in the board, but the critical ECC part just won't work. So, if you want to try for 128GB or 256GB total memory, you can, but keep the receipt if you have to return it.

Max memory speed on the Xeons is a mixed bag. 16xx (v1/2) Xeons allow for overclocked memory (like the 2400 you mentioned, but again, YMMV if it can handle it), but 26xx (v1/2) Xeons are memory multiplier locked, meaning Sandy Bridge EP has a top speed of 1600MHz and Ivy Bridge EP is 1866MHz.
 

SLP Firehawk

Weaksauce
Joined
Jan 30, 2020
Messages
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Wow thank you for the very very helpful info! This gives me some things to think about.
One thing for sure is I do want 64GB RAM. More would be even better but I do not want to go less than 64
 

E4g1e

Supreme [H]ardness
Joined
May 21, 2002
Messages
7,253
That's a tough question to answer. The X79 chipset and its accompanying processors officially support memory speeds up to DDR3-1600. And with your i7 you will officially have to fill up all eight DIMM slots with 8 GB DIMMs in order to attain 64 GB total RAM. This is because there are absolutely no unbuffered non-ECC 16 GB DDR3 DIMMs in existence. The use of 16 GB DDR3 DIMMs require them to be both registered and ECC, something that no i7 officially supports, and relatively few X79 BIOSes ever released have the capability to even enable either of those two features even with a Xeon CPU.

And Xeons do not necessarily require registered or ECC RAM, but they prefer that you do use registered ECC RAM.
 
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