Does quad channel memory addressing scale back to dual channel or single channel?

[UnicornU]

Hi guys

I have a dual processor motherboard and 4x16 GB memory modules
My MB (Asus KGPE-D16) supports quad channel.

Wikipedia says that"
DDR3 Quadruple-channel architecture is used in the AMD G34 platform and the Intel LGA 2011 platform (e.g., Intel X79 or Intel X99). AMD processors which are used on the C32 platform instead use dual-channel DDR3 memory. Intel processors which are used on the LGA 1155 platform (e.g., Intel Z68) instead use dual-channel DDR3 memory.

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.[15]

This very interesting thread tells me that in the worst case scenario I could end up with four modules workin in single channel mode

I m not sure what would happen in my case if quad channel mode fails.
Since I have 3x16GB is there any way to install these to work in triple channel mode?
The manufacturer has this map that one should use to install memory modules

What is not clear for me is how the channels form and if this map is mandatory.
Wikikepedia says that you could have triple channel but I can't see that happening with that mapping. How can you split three modules between two processors ? I don;t think that this motherboard can take an odd number of modules

However let's say I have my modules 3+1. If quad channel fails does this mean that I might end up with this:
1 dual channel (2x16G identical) for one CPU
2 single channel (1x16G and 1x16G) for the other CPU?

What happens when you add more RAM? Let's say I buy another set of 4 modules, this time this will be a kit of 4 identical ones. Will these work in 4 channel mode if the system already has 1 dual channel and 2 single channels active ?

 

[kanewolf]

Notice NOWHERE on the manufacturer's list is three DIMMs shown... They obviously don't recommend three DIMMs period.

 

[UnicornU]

Yeah that is clear to me too
The question is what happens when you have a mix of chips, either the same capacity and different chipsets or different capacities and different chipsets

I have a couple of threads in this forum that are related to the first case (3x16G in a kit, and 1x16G as single module, almost identical -same params but different chipsets; essentially all that is missing is a RAS timing discrete value which is not present for one of the chipset, othewise they seem completely identical)

My question is, if I take the risk to install them as they are what will I end up with and what is the possible impact on future RAM additions that I am planning (I will have 64G and the MB supports up to 256GB)

 

[kanewolf]

If you want to do this as a "science experiment" then go for it. If you want a server that you can depend on follow the manufacturer's advice...

 

[UnicornU]

If you want to do this as a "science experiment" then go for it. If you want a server that you can depend on follow the manufacturer's advice...

Which manufacturer memory or MB???
The MB manufacturer does not list any of the kits that I bought

The memory manufacturere explicitely lists KVR13R9d4/16 as compatible
The other kit is actually very similar with what would be 3x KVR13R9d4/16 but with slightly different chipsets
The memory manufacturer support person told me that the chispets used for modules are almost identical and they will likely work in a quad channel mode.
I want to know what happens if the CPU can not establish a quad channel communication with the memory modules, what is going to happen? Does it fall back to dual/single channel ? How does this impact the future planned upgrades.

I know that if I follow the manufacturer directions I will get there but ..I will be more like a monkey, I will not understand why and what.

 

[kanewolf]

I would ALWAYS follow the MB recommendations for supported memory models and configurations especially if you intend to depend on this server for $$$. Just my opinion ....

 

[mdocod]

If you have 2 CPU sockets, and 2 CPUs installed, then you have 2 separate memory controllers. In order to run in quad channel on both CPUs, you would need no less than 8 RDIMMs.

If I understand correctly, you have 3 matching RDIMMs, and 1 that is similar.

You should install 2 RDIMM's in slots mapped to the first CPU, and 2 RDIMM's in slots mapped to the second CPU. Provided the mismatch doesn't create any problems (rarely would there be an issue with "mismatched" dimms when working with enterprise grade memory as it conforms to much better standards), you will have a dual channel memory configuration on each CPU.

Sorry, you don't have enough RDIMM's to run quad channel memory on a dual socket system.

 

[UnicornU]

Interesting that the Kingston guy did not say anything about having to have 4 memory modules for each processor.
Yes what you are saying makes a lot of sense.
However since then I managed to swap the 3+1 combination for 4 identical (not bought as a kit though) and not I am having trouble with getting them to work at least in dual channel (I just learned this after reading the above) Please see this http://www.tomshardware.com/answers/id-2488156/4x16g-indentical-modules-working-quad-channel-mode-adjust-bios-improve-situation.html