Question Do motherboards actually have RAM capacity limits ?

[Genralkidd]

I've been shopping around for an LGA 2011 X79 motherboard to use with a Xeon CPU I have and I currently have 128 GB of DDR3 ECC RAM on hand too. However I've noticed that a lot of listings I've seen for X79 motherboards have inconsistent information for the max supported RAM. Some sellers listings of those boards say up to 128 GB while others say up to 64 GB. Even some listings have both max sizes listed too. So do motherboards actually have a max RAM size regardless of having the same chipset? Or can i safely ignore the 64 GB RAM limits and should be fine going up to 128 GB?

 

[Lutfij]

Take this motherboard as an example;

GA-X79-UD3 (rev. 1.0) Specification | Motherboard - GIGABYTE Global

Lasting Quality from GIGABYTE.GIGABYTE Ultra Durable™ motherboards bring together a unique blend of features and technologies that offer users the absolute ...

www.gigabyte.com

GA-X79-UD5 (rev. 1.0) Specification | Motherboard - GIGABYTE Global

Lasting Quality from GIGABYTE.GIGABYTE Ultra Durable™ motherboards bring together a unique blend of features and technologies that offer users the absolute ...

www.gigabyte.com

see the difference in the ram supported and the slots on the motherboard?

So yes board will have a limit on ram supported.

 

[Genralkidd]

Take this motherboard as an example;

GA-X79-UD3 (rev. 1.0) Specification | Motherboard - GIGABYTE Global

Lasting Quality from GIGABYTE.GIGABYTE Ultra Durable™ motherboards bring together a unique blend of features and technologies that offer users the absolute ...

www.gigabyte.com

GA-X79-UD5 (rev. 1.0) Specification | Motherboard - GIGABYTE Global

Lasting Quality from GIGABYTE.GIGABYTE Ultra Durable™ motherboards bring together a unique blend of features and technologies that offer users the absolute ...

www.gigabyte.com

see the difference in the ram supported and the slots on the motherboard?

So yes board will have a limit on ram supported.

It's hard to tell then cause a lot of the boards I'm looking at are all similar 4 slot boards on AliExpress. And different sellers of the same board will have different max memory listed. Some sellers list it as 64 GB while other sellers list the same board as 128 GB max. Some of the boards also appear to be unbranded too so I can't find any manufacturer documentation on the actual max memory size.

What would happen if I exceed the motherboard's max memory size? Would it just refuse to boot or something?

 

[CountMike]

It's hard to tell then cause a lot of the boards I'm looking at are all similar 4 slot boards on AliExpress. And different sellers of the same board will have different max memory listed. Some sellers list it as 64 GB while other sellers list the same board as 128 GB max. Some of the boards also appear to be unbranded too so I can't find any manufacturer documentation on the actual max memory size.

What would happen if I exceed the motherboard's max memory size? Would it just refuse to boot or something?

There's another RAM capacity limiting factor and that's CPU. Memory controller is in CPU and has 2 or more memory channels each one supporting so much memory. MB manufacturers limit the number of slots according to best CPU it supports. For consumer type of MB and CPU they are artificially limited to certain (bellow theoretical) amount to leave space for much more expensive CPUs and systems like for servers etc.

 

[Genralkidd]

There's another RAM size limiting factor and that's CPU. Memory controller is in CPU and has 2 or more memory channels each one supporting so much memory. MB manufacturers limit the number of slots according to best CPU it supports. For consumer type of MB and CPU they are artificially limited to certain (bellow theoretical) amount to leave space for much more expensive CPUs and systems like for servers etc.

The CPU I'm using is the Xeon E5 2696 V2 and to my knowledge it shouldn't have any problems with 128 GB of ECC RAM. So even if the CPU supports the RAM capacity I want, the motherboard itself could still be artificially limited to a lower amount and refuse to POST when there's more RAM?

 

[CountMike]

The CPU I'm using is the Xeon E5 2696 V2 and to my knowledge it shouldn't have any problems with 128 GB of ECC RAM. So even if the CPU supports the RAM capacity I want, the motherboard itself could still be artificially limited to a lower amount and refuse to POST when there's more RAM?

It supports max of 768GB of DDR3 so you should have no problems with 128 providing MB has enough slots and/or can find larger RAM sticks.

 

[Genralkidd]

It supports max of 768GB of DDR3 so you should have no problems with 128 providing MB has enough slots and/or can find larger RAM sticks.

Thanks for clearing that up! Just one more question before I order a motherboard. So one specific example is the Asus Sabertooth X79 motherboard. It has 8 slots for RAM on the motherboard but the manufacturer's manual says the max supported RAM is only 64 GB of RAM. The Xeon CPU I'm using should be supported though and the manual mentions ECC support too. So does that mean I can just ignore that and assume that motherboard will support 128+ GB of RAM despite what the manual says?

 

[boju]

What will you be doing that'll require so much ram?

 

[CountMike]

Thanks for clearing that up! Just one more question before I order a motherboard. So one specific example is the Asus Sabertooth X79 motherboard. It has 8 slots for RAM on the motherboard but the manufacturer's manual says the max supported RAM is only 64 GB of RAM. The Xeon CPU I'm using should be supported though and the manual mentions ECC support too. So does that mean I can just ignore that and assume that motherboard will support 128+ GB of RAM despite what the manual says?

At the time MB was released DDR3 was pretty well limited to 16 GB sticks and 8GB/stick max. That might be the reason for 64MB limit. See if there's a BIOS that can use 16GB sticks.
Worst that can happen is that only 64GB may be recognized with only 8GB per stick. At this time you might need a dual CPU MB for that much RAM