Windows 10 sees only 3 memory modules out of 4 while CPU-Z sees them all

Question

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":

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

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

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.

Answer 1

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.

Answer 2

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.

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.

Answer 3

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.

Answer 4

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.