PC not making use of all RAM

[woolfe9998]

OK this is a problem I've literally been troubleshooting off and on for 2 months. Built a new PC back in early Feb, Asrock x370 Pro4 mainboard, 4 dimm slots. I put 4x4 identical Viper DDR4 3333 into the 4 slots. In Windows 10 (64 bit), it says I have 16gb RAM (8 gb useable). The BIOS recognizes and correctly identifies all 4 sticks. But Windows won't use more than 8gb even though it sees 16gb.

There are two well recognized fixes in Windows for this, one is a setting that specifies maximum useable RAM. That is set correctly at 16 gb and change. The other has to do with a "page file" setting or something like that. Already done it. Doesn't work. Also, I now have a new SSD with a fresh Win10 install, but the same problem exists. So it's either hardware or BIOS settings.

The third known solution is going into the BIOS to shut off the onboard video. Can't be done in this BIOS. I've looked over everything in it for a long time and it just isn't there. But I can almost guaranty that wouldn't fix it either, because of this:

I played around with different RAM configurations. All 4 DIMM slots work. I can put 2 sticks in any 2 of the 4 slots and the 2 sticks work fine. But I can also put an 8 gb stick into 1 slot and a 4 gb stick in another, and presto, I get 12 gb useable RAM. Which means Windows is only able to use RAM from ANY 2 DIMM slots, but will not use any in other slots beyond 2. The RAM amount isn't capped; the number of useable DIMM slots is.

I can get 16 gb useable now if I go 8x8 in 2 slots, but at some point I'm going to want to use the other slots. I feel like the solution is somewhere in the memory settings in the BIOS, but I don't understand what any of it really means. Is it something to do with "interleaving?" I figure some of you have a better understanding of memory settings in the BIOS than me.

 

[VirtualLarry]

Your board is simply defective; RMA it.

Edit: Or your RAM is. One of the two.

Edit: You won't be able to run your RAM at 3333 in all four slots, most likely. Try adjusting RAM clock in BIOS to 2400, with all RAM installed?

 

[woolfe9998]

It's definitely not the RAM itself. Each stick works independently. Might well be the board, maybe the memory controller on it is bad, making it so you can't use more than 2 DIMM slots at a time. I'll try your suggestion of lowering the mem speeds.

 

[VirtualLarry]

The thing about the RAM / RAM "Usable" thing is, the "RAM" amount, is detected via the SPD info on each DIMM. That tells the host PC what capacity DIMM is in each slot.

But then, the BIOS/UEFI "probes" the RAM, to see what RAM is really there and accessible. That's where things can get wonky.

I had an FM1 board, and a pair of Kingston DDR3 DIMMs, and I was overclocking the APU slightly, and had some issues with DIMM detection, I had to re-seat and tweak the OC several times to get it all recognized.

Are you OC'ing at all? Remember, a RAM clock of 3333 is still OCing too.

What CPU/APU are you using? I don't think that you've said that yet. Look up the RAM speed specs, for 2 and 4 DIMMs, for that CPU/APU family, and try setting your RAM clock to that.

Also, consider flashing your BIOS/UEFI to newest, especially on AM4 platform, they have done a lot for memory-compatibility with newer BIOS revisions.