Windows 10 seeing but ignoring one RAM slot

Question

I'm not sure what is wrong here.

Looking online it says that one RAM stick might be bad, but if that was the case my OS wouldn't be able to interface with its hardware.

As you can see in the picture below my 8gb stick is not usable. (Slots 1-3 are all the same type of stick) In total I have 3, 4gb sticks and 1 8gb stick.

Motherboard: ASUS M5A99FX PRO R2.0 AM3+ AMD 990FX (Supports 1866/ 1600/ 1333/ 1066

The missing RAM (Slot 4 below): Ballistix Sport 8GB (Speed 1600 MT/S)

What am I not understanding? How can I get my os to use all the installed RAM?

My chipset: AMD 990FX + SB950 supports up to 32gigs of ram

Solution

There could be a few reasons why your memory isn't usable.

First things first:

• It's not a good idea to mix-and-match your RAM, different sizes and vendors.
  • It can lead to system instability
  • In your case, you will encounter decreased performance (even if you do get the extra memory mapped) because you will not benefit from a dual-channel configuration see: What is dual channel memory?
  • If you do mix and match ALWAYS do it in pairs.

Note, that the color-coding on your motherboard RAM slots is not just for "kicks", the color pairing are the two channels (A and B) that your motherboard owners manual refers to. If you do install different sized RAM chips, do it in pairs, matching the Channel with the set. This is probably the #1 reason why it's not usable to your system.

A quick way to test my theory would be to remove the other smaller 4GB stick in the matching color of the 8GB stick and try to boot your system. If all goes well, you'll now see 16GB usable, instead of 12GB. If so, then your best option is to buy another of the 8GB sticks (same brand and model). You should then be able to use that full 24GB.

The owners manual of your motherboard states:

You may install varying memory sizes in Channel A and Channel B. The system maps
the total size of the lower-sized channel for the dual-channel configuration. Any excess
memory from the higher-sized channel is then mapped for single-channel operation.

I also want to point out that the RAM you have is not listed in your motherboard's Qualified Vendors Lists (QVL). While this is not an exhaustive list of RAM that is compatible with your MB, it is a list that signifies what was tested with your MB. Going out of these bounds is more of an "at your own risk" sort of grounds.

Windows also has some reasons as to why it may not be mapped (for 7, but it should still apply to 10 as well): https://support.microsoft.com/en-us/help/978610/the-usable-memory-may-be-less-than-the-installed-memory-on-windows-7-b

Comments

[Ramhound]

Since they don’t make 20 GB modules, how much memory, is supposed to be detected? Your question doesn’t indicate this information

[Gabriel Fair]

20gb is supposed to be detected, I mention that I have four slots each with a stick of ram. My 8gb stick isn't being detected

[Ramhound]

20 GB so you have 8 GB and three 4 GB modules...?

[Gabriel Fair]

Yes, I'll make that more clear in the question. Thanks

[arielnmz]

I disagree about mixing RAM from different vendors [is] not well supported from a technological standpoint, since all vendors must fully comply with a standard.

[CenterOrbit]

@arielnmz That's true; but sticking with the same vendor/model ensures that all of the intricacies (such as voltage, and RAM timing) are the same for all sticks being used. Easier for the BIOS to just get up and running with. I've def used different vendors mix/mashed.

[arielnmz]

Those intricacies are also part of the standard, that point just makes no sense.

[CenterOrbit]

You know, you're right. I updated my answer to remove that line. Thanks, @arielnmz

[I say Reinstate Monica]

Please explain how reseating the CPU will make it suddenly start using memory it obviously already has a working electrical connection to. This makes no sense.

[Gabriel Fair]

Thank you for this. I found it helpful

[Admin]

@IsayReinstateMonica Maybe he had touched the RAM slots.