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I have 4 DDR4 memory modules 8 GB each, in total 32 GB. CPU: Intel Core i9 7900X. Mainboard: X299 DESIGNARE EX-CF.

I have used Windows 10 Professional on this computer and it saw all 32 GB RAM.

Later, I have reinstalled Windows Professional. I have installed latest Windows 10 version 1809 (build 17763.437).

The problem is: now Windows 10 it sees only 3 memory modules out of four, and thus only 24 GB RAM.

The Windows Task Manager shows "Slots used: 3 of 8":

Windows 10 Task Manager

In the same time, CPU-Z shows that all 4 slots are present:

Slot#1 Slot#2 Slot#3 Slot#4

In the same time, CPU-Z shows that "Channel#" is "Triple" (not "Quad" as before):

Triple Channel

How can I make Windows 10 see all the memory modules and 32 GB total?

If I run “Windows Memory Diagnostic” from the Control Panel Administrative tools, it reboots the computer, does memory checks, then reboots it again and doesn’t show anything, while it appears the following record in the Event Log: “The Windows Memory Diagnostic tested the computer's memory and detected no errors”.

BIOS shows that all 4 modules are present 8 GB each, 32 GB total.

Since “Windows Memory Diagnostic” shows no errors, I can assume that all 4 modules are functional. I could assume that one of the modules could fail, but since BIOS sees them all and CPU-Z shows distinct Serial Number for each of the modules, and The Windows Memory Diagnostic sees no error, it can lead to a conclusion that all 4 modules are OK. I don't have spare modules to test. How should I proceed?

I have also updated BIOS firmware to the latest version to date but it did not help. Besides that, Windows 10 in the past saw all 4 modules even with the old BIOS version.

I have searched Microsoft website for the probable limitations of Windows 10 Professional and didn't find anything that Windows 10 Professional could have had any limitation on 3 memory slots or whatsoever number of memory slots. It only had a limit on number of terabytes of memory which I'm far from reaching.

Maxim Masiutin
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    The most important point is: Does the firmware setup show the correct amount of memory? – Daniel B Apr 29 '19 at 16:48
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    Is each module itself functional? In order to determine this, you must remove, all but a single module. Instead of a comment, edit your question, to include this vital information. – Ramhound Apr 29 '19 at 16:51
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    Your issue is that your memory is in triple channel configuration instead of dual channel. You have a memory module installed on the wrong channel. reference your motherboard manual for the proper dual memory configuration. You should still test each module by itself. – Ramhound Apr 29 '19 at 17:29
  • @Ramhound - I have installed memory modules correctly, according to the mainboard manual. In the past, Windows 10 saw all 4 memory modules. I didn't replace the modules since then, only reinstalled Windows. Should I add more information to the question? – Maxim Masiutin Apr 29 '19 at 17:31
  • Your problem is similar to those in single channel configuration instead of dual-channel configuration. I believe you have a hardware problem, which is the reason, testing each module individually is important – Ramhound Apr 29 '19 at 17:36
  • @Ramhound - do you mean that I can try to get all 4 new modules and try to install them hoping that Windows will finally accept them all? – Maxim Masiutin Apr 29 '19 at 17:38
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    @MaximMasiutin - Start by installing a single module, see if that works, rinse and repeat through the other 3. If all four modules work by themselves, install each individual module, verifing it is detected before moving on. Be sure you install them in the correct slot in order to achieve the proper memory channel configuration. – Ramhound Apr 29 '19 at 17:50
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    Your screen shots show slots 1-4 as in use, but per the manual you should be using every other slot of the mother board. I would just double check that and make sure its correct. – Patrick Apr 29 '19 at 18:11
  • It is the CPU-Z that shows slots this way. BIOS shows that slots 1,3,5,7 are used. Anyway, even if memory modules are put in incorrect slots, Windows should have seen all memory (32 GB), although not in QUAD-channel mode. – Maxim Masiutin Apr 29 '19 at 18:20
  • It seems that the CPU can only handle 4 memory channels while you have 4 dual-channel sticks, which seems somewhat contradictory. Please make this test of temporarily disabling the pagefile in Control Panel > System > Advanced system settings > Performance > Settings > Advanced > Virtual memory > Change, uncheck Automatically manage paging file size for all drives, finally select each drive on the list and choose No paging file, then reboot. Return the above check-mark if no change. – harrymc Apr 29 '19 at 19:17
  • Since in the past Windows and BIOS worked properly with the same hardware setup, but then at an unknown point of time Windows saw only 3 modules out of 4 while I didn't open the computer case (only reinstalled Windows), I don't think that the problem might have been with hardware configuration (memory module layout). – Maxim Masiutin Apr 30 '19 at 07:44
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    I have followed Rahmound's advice and tried to boot computer with just one memory module at a time (detaching other 3). It booted OK with each of the 3 modules out of 4, but with one of the modules BIOS even didn't start. The LED on the motherboard showed "55". For Gigabyte motherboard it is Error 55 "Memory Initialization Error". So I have removed that faulty module and left other 3 good modules. Windows again shows 3 modules out of 8, 24 GB RAM, and CPU-Z shows again that memory channel is Triple. I will try to get a replacement module and let you know how it works with all 4. – Maxim Masiutin Apr 30 '19 at 07:48
  • There is also a probability that it is the memory slot in the motherboard that got faulty, not the module itself. I didn't try to install that module into other free slots. I will get a replacement module this week and will let you know what was wrong. – Maxim Masiutin May 01 '19 at 14:19
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    After receiving a replacement module, I have found out that all 4 modules were OK. It was a mainboard slot that stopped working. Even the new module didn't work in that slot. However, all 4 old modules worked well in another motherboard. So I'm now using just 2 new modules Kingston DDR4 KHX3333C16D4/8GX Week 07/Year 19 (in dual-channel, not a quad-channel, unfortunately, as before) in the X299 DESIGNARE EX-CF motherboard. – Maxim Masiutin May 07 '19 at 20:31
  • @MaximMasiutin - Why did you offer a bounty on a question due to a hardware problem with the motherboard? – Ramhound May 07 '19 at 20:37
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    I think it may be a common problem. Other users might have experienced it as well. Problem is that CPU-Z saw all modules while Windows did not. We may give an answer here on how to diagnose and solve the problem, as you did. – Maxim Masiutin May 07 '19 at 21:04
  • As for me, the problem is completely solved. All what I want is to share the knowledge with the other people. That's why I have proposed a bounty since we don't have an answer. – Maxim Masiutin May 07 '19 at 21:05
  • @Ramhound - could you please summarize all your comments (and my replies) to the formal answer? – Maxim Masiutin May 07 '19 at 21:06
  • @Ramhound - so I could give you +100 bounty? – Maxim Masiutin May 07 '19 at 21:06
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    @MaximMasiutin - You should have just submitted an answer yourself instead of offering a bounty to a bunch of people that don't need more reputation. – Ramhound May 07 '19 at 21:12
  • @Ramhound - thank you! I have made a summary of the comments as a separate answer. I hope it will be useful to the community of superuser.com visitors and those who get here using a search here. – Maxim Masiutin Sep 15 '20 at 18:22
  • @DanielB - I have posted an extended answer that shows steps to resolve the problem. The answer is here, it has sections like "Step 1: Locale faulty module" and so on. – Maxim Masiutin Sep 22 '20 at 18:11

4 Answers4

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The problem is: now Windows 10 it sees only 3 memory modules out of four, and thus only 24 GB RAM.

Since each module is functional by itself you have confirmed the problem is not one of the memory modules.

After receiving a replacement module, I have found out that all 4 modules were OK. It was a mainboard slot that stopped working. Even the new module didn't work in that slot.

You can get around your hardware issue by using 16 GB DDR4 modules instead of 8 GB DDR4 modules.

Ramhound
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Assuming that windows checked all of the memory is an invalid assumption. It only reports that there were no errors on the memory it checked, which may be only the 24GB, not the full 32GB.

You should check the user manual for the motherboard as the memory sticks need to be inserted in the slots in specific arrangements in order to function properly. If they are installed correctly, try reseating each stick (with the power off of course).

Boot to a linux live OS (where the OS lives on your USB stick) and see if the problem persists. If it does then the problem has nothing to do with your operating system. The free, open source software I linked has memtest86+ as an available boot option. It also has a system info tool in the GUI if you boot with default selection. You should be able to use either tool to verify whether the system is seeing 24GB or 32GB.

enter image description here

If the memory is installed according to the specifications in the user manual and you can't get it to show in the linux live OS, then I suspect that you probably have a bad RAM slot on the motherboard and that it will need warranty repair/replacement. I had a similar problem on an MSI x299 board.

apocalysque
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The most probably answer in such cases is that either memory module or motherboard slot is faulty. To locate the problem, follow these steps:

Step 1: Locate the faulty module

(by the end of next step you will know for sure whether it is the module that is faulty, or the slot in the motherboard)

Remove memory modules one by one and reboot the computer to see how much memory does Windows see. Just one module at a time should be removed, and when proceeding to the next module, previous module should be put back, to the same slot. Do not mix memory modules between slot to avoid damaging a module in case of a faulty slot.

If after removing the module Windows sees less memory, than this module (or slot) is good. Otherwise, if removing a module does not change total amount of memory, than this module (slot) is faulty, and Windows does not use it anyway.

Step 2: Get the replacement module

Get a replacement memory module and put it at the same slot. If Windows starts seeing all the modules and the total memory size is the complete sum of all modules, than the replaced module was bad. If replacing a module does not help, than the problem is likely in the motherboard slot, not in the module.

If during this step, even after replacing a memory module, Windows still does not see all the memory, then the problem is most likely in the motherboard. In this case, proceed to step 3.

Step 3: Replace the motherboard

(you will only need to be at these steps in case of previous steps did not completely solve the problem)

When filling memory slots of the new motherboard, do not put the old, replaced, module (that you supposed to be faulty) to the new motherboard, put the new module instead, just in in case that that the old module have damaged the slot of the old motherboard – in this case it can damage the slot of the new motherboard too.

Now Windows should see all the memory!

Step 4 (optional): Put the old module to the new motherboard

This step is optional and risky. The risk is that if it was the module that damaged the slot of the old motherboard, it may damage the slot of the new motherboard too. So you will end up with one faulty module and one faulty motherboard. But if you take this risk and win, you will: (1) be able to return the new module, and (2) know for sure that it was the motherboard slot that got broken by its own, not the memory module. So it was in my case. I have returned the old slot so the new motherboard had all old modules – and Windows saw all the memory. So it was the memory slot that ceased functioning in my motherboard, and that was the reason – I had to replace the motherboard to have Windows see all the memory.

The above steps is a useful algorithm that allowed me to diagnose and resolve the problem.

Maxim Masiutin
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Try loosening your CPU cooler a touch.

Just had the exact same thing happen on the exact same motherboard. Memory was seen in BIOS but only 3 of 4 in windows.

JNCS
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