I am to purchase RAM for my newly purchased

I want to max out the memory to 64GB and planned to puchase four

  • 16GB ECC unbuffered/UNB/UDIMM RAM.

The memory I am interested in is

The question is whether the SAMSUNG memory is compatible with the ASUS motherboard.

Samsung's Support > Tools & Utilities > Board Compatibility is not helpful, and strangely does not even list DDR4 memory.

The QVL (Qualified Vendor List) for memory from ASUS does not list M391A2K43BB1-CPB.

Two other Samsung memories are however listed 16GB DDR4-2400 Non-ECC/UNB and 8GB DDR4-2133 ECC/UNB CL15; the first not fit for the CPU, and the second will only max out to 32GB.

The only two vendors that are on the list with an acceptable memory specification 16GB DDR4-2133 ECC/UNB CL15 are INNODISK and Skhynix. Neither of which are available to me for purchase.

I found however that the QVL for memory for the ASUS P10S-M motherboard lists the Samsung M391A2K43BB1-CPB.

I noticed that the memory chip for the listed Samsung M391A2K43BB1-CPB is the same memory chip listed for the INNODISK memory chip; Samsung K4A8G085WB-BCPB.

There are multiple memory companies on the market, but only a few true memory manufacturing companies. When researching different memory brands, you may run across companies that claim to be memory manufacturers, when they're really just module assemblers. How these companies work is that they purchase pre-manufactured parts (such as DRAM chips and printed circuit board) from true memory manufacturers, and then assemble these components to “manufacture” a module with their label on it.

If I understand correctly, the listed P10S-M WS/IPM-O INNODB M4CR-AGS1MC0G-BE93 is actually more or less the same memory as Samsung M391A2K43BB1-CPB?

Even if they would differ for some reason, I am having a very difficult time to accept that the M391A2K43BB1-CPB -- or really any other memory -- will be incompatible with the motherboard save for some edge cases, such as incorrect manufacturing or assembling.

As this is my first build it would be assuring if someone could confirm my conclusion.

  • This is almost a tech support question (off-topic), are you open to other makes/models that are compatible? – user1691 Oct 20 '17 at 15:22
  • If it can be explained why they would be compatible, then yes. The general question of interest is how to determine compatibility, and I am using my case as an example. Generalizing my case it would seem that if a motherboard manufacturer approves memory from vendor X with chip Y then any other memory provider Z with the same same chip Y should satisfy compatibility. Having said that, this question should qualify as "A request for information that will lead to a product decision", no (hardwarerecs.meta.stackexchange.com/questions/205/…)? – user212827 Oct 20 '17 at 15:54
  • Re the scope of question Pre-Purchase Questions → Assurance You're Making an Informed Decision (hardwarerecs.meta.stackexchange.com/questions/139/…) – user212827 Oct 20 '17 at 15:58
  • @SiXandSeven8ths please also note that the other models in the QVL either did not satisfy my requirement (16GB DDR4-2133 ECC/UNB CL15) or are are not available to me. – user212827 Oct 20 '17 at 16:09

The question What exactly is the cause of RAM incompatibility? on superuser provides a good overview of possible causes for incompatibility. The answers to the question provide some interesting reasoning.


You might have two RAM sticks with the same part number and one can tolerate a 5% undervoltage and the other can't, and the mobo might put out a low voltage because it's poorly calibrated. But, again, this is very rare now. Sane combinations almost always work. Before DDR2, it was a mess. After DDR2, it was sufficiently standardized.

In the follow up discussion https://chat.stackexchange.com/rooms/65926/discussion-between-david-schwartz-and-ehryk

These days, it's almost always the obvious incompatibilities. That is, if it doesn't work, you can usually figure out why. When you can't, the most likely explanation is that some part is just crappy.

In the old days, weird incompatibilities were not that unusual. But since the DDR2 standard, cases of incompatibility not involving one of the explanations mentioned are fairly rare. Most of those cases are likely to be components that are not quite meeting their specifications.

From another answer https://superuser.com/a/1252995/774206

I built many systems throughout my career and I have not once looked at the supported RAM list before I chose the components. And I have never had any incompatibilities so far. That being said, the list can give guidance to beginners and less experienced people to select the correct components to build a good working system.

From another answer https://superuser.com/a/1252617/774206

The answer lies within the memory controller. The memory controller used to be on the north-bridge of the motherboard. It had to negotiate all the features that the CPU supported for direct memory access. So the CPU is really the determining factor that limited what memory you could use even though it appeared to be a motherboard capability. This is more obvious now that the memory controller lives inside the CPU in all modern chips made by Intel, AMD, and ARM. The motherboard firmware contains microcode from the CPU manufacturer that dictates what kind of features for direct memory access it supports. So the software still lives in the motherboard but the hardware is in the CPU now.

The clocking of CPU and Memory are directly linked through the Base Clock. They have to be multiples of each other in sync. Aside from that the details of Direct Memory Access are non-trivial and I will not attempt to explain here. My understanding is that just like MB and CPU manufacturers have different implementations and features, so do different memory modules. Within one memory manufacturer, like Kingston, the actual chips could be made by Samsung, Hynix, or someone else. They should all follow a spec but maybe they don't implement every feature the same way.

While no answer was accepted, one was given the "bounty"; https://superuser.com/a/1252970/774206. The answer provides some examples of what may cause incompatibility.

Using the

I have tried to create a comparison table. Mainly for the fun of it :)

My best [uninformed] guess is that with the new CPUs, motherboards and memories the main criteria for memory compatibility is the common referred specifications, and any incompatibility issue is mainly due to "bad luck".

            |      INNODISK      |      SK HYNIX      |      SAMSUNG     |
            | M4CR-AGS1MC0G-BE93 | HMA82GU7MFR8N-TFT0 | M391A2K43BB1-CPB |
            |                    |   (revision 1.2)   |                  |
    chipset |  K4A8G085WB-BCPB   |  H5AN8G8NMFR-TFC   |K4A8G085WB-BCPBM00|
   bandwith |     2133 MT/s      |      2133 MT/s     |     2133 MT/s    |
  frequency |    (1066.67MHz)    |    (1066.67MHz)    |      1066MHz     |
    voltage |        1.2         |         1.2        |        1.2       |
       rank |       Rank 2       |       Rank 2       |       Rank 2     |
    density |       16GB         |     16GB (2Rx8)    |    16GB (2Gx72)  |
            |                    |1Gx8(H5AN8G8NMFR)*18|1Gx8(K4A8G085WB-BC##)*18|
    timings |====================+====================+==================|
 cycle time |       0.93ns       |       0.93ns       |       0.93ns     |
   tCK(min) |                    |       0.937        |       0.938      |
         CL |         15         |         15         |        15        |
  tRCD(min) |                    |    14.06 (13.50)   |     15 (14.06)   |
   tRP(min) |                    |    14.06 (13.50)   |     15 (14.06)   |
  tRAS(min) |                    |         33         |         33       |
   tRC(min) |                    |    47.06 (46.50)   |       47.06      |
        CMD |                    |                    |                  |


I purchased the M391A2K43BB1-CPB and installed it; the computer boots without any errors, and no errors are reported after test:

  • running MemTest86 (v7.4) 4 to 5 passes (~12h),
  • running stressapptest (v1.0.8) stressapptest -W -s 3600.
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