DDR4: 32GB in slots. Work only 24GB

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dusan.chlud

Feb 23, 2018
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Hi, I have 4x8GB DDR4 in slots, but BIOS, and system shows only 24GB to use.

BIOS see 4 slot with 8GB on each in use, but show only 24GB avaible. CPU-Z the same.

I was test RAM - OK
Each DDR module works alone well in all different slots. And that's blows my mind.

Even If I tried complete modules in sequence. First was ok. But two modules shows still 8GB. I tried different modules in different slots. 3 modules shows 16GB and 4 modules 24GB.

Any Idea?

X299 GAMING M7 ACK
2x Corsair Vengeance LPX DDR4 16GB (2x8GB) 3000MHz CL15
i7 7800X
 
Solution
jr9
There is no ascertainable reason for it that I can see. If it doesn't work properly with two DIMMs then that generally indicates an issue with the motherboard or one of the RAM modules. It should be able to work with two DIMMs.
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dusan.chlud

Feb 23, 2018
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Thank you for the quick answers guys.
Newest BIOS not help with this. Screenshot of it - 4 slots he see, but not work with.

Buy new modules for test is good idea. At monday I'll try it.
 
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dusan.chlud

Feb 23, 2018
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No. I got 2x CMK16GX4M2B3000C15, but they have also CMK32GX4M4C3000C15 .. So in my opinion, this isn't that problem. And as I wrote in first post - one and two modules in slot is the same in BIOS. Still showing 8GB available. BIOS shows two slots in use, but whole memory is half. And It does with random my modules in random slots.
1 module - 8GB for use
2 module - 8GB for use
3 module - 16GB for use
4 module - 24GB for use
 
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jr9

jr9

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Dec 6, 2017
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Ok, so did you try just the two Corsair ones in slots A1 and C1? You have 8 RAM slots on that board so they must be populated in a certain way. For 4 channel, you need the sticks in:

B1, A1, C1, D1

or

Slot 1 on left side of CPU, slot 3 on left side of CPU, slot 2 on right side of CPU, slot 4 on right side on CPU

DIMM1 - Empty - DIMM2 ---- EMPTY [CPU Cooler] Empty ----- DIMM3 ------EMPTY -----DIMM4 = 4 DIMM setup

Empty - Empty - DIMM1 ---- EMPTY [CPU Cooler] Empty ----- DIMM2 ------EMPTY -----Empty = 2 DIMM setup

The slots may not work if you are plugging the DIMMs into random slots.
 
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dusan.chlud

Feb 23, 2018
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B1,A1,C1,D1 is my setup. As screenshot in my post earlier. I tried 2 modules as you said, but. Still the same - viz screenshots. Upper you see Memory size -8GB, but BIOS see modules correct. I tried switch modules, so, all of that works.


 
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jr9

jr9

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Dec 6, 2017
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Good info. The 2 DIMM configuration was done with the CMK16GX4M2B3000C15/Corsair 2x8GB kit? If so and you have the latest BIOS I would:

- Try an individual DIMM in A1 and C1 although I think you did this already. Also try installing A1 and C1 together using extra insertion force.

- Try setting the RAM to a higher speed using XMP. A little extra voltage can help when RAM won't detect. You can also up the voltage slightly manually.

- Check the CPU socket for bent pins. Bent pins in the socket can cause memory detection problems

- RMA the motherboard.

If you can't get the 2x8GB to detect and that's part of a kit then it's the motherboard's fault even if the 2x8GB kit isn't on the QVL. Not getting dual channel or over 2133MHz is one thing but complete failure to detect RAM generally isn't the RAM's fault if you proved the RAM works one at a time.
 
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dusan.chlud

Feb 23, 2018
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Difference between CPU-Z and Win [screen]. The same showing monitoring soft from MSI MB.. wtf..



- XMP doesn't help. MB detected it with or without XMP. But not whole memory. I tried reset CMOS again and after it - BIOS show using QUAD CHANNEL in 24GB memory.
- modules is extra forced in - none difference
- each one works alone
- There is deep night here in Czech Republic. I will insert CPU again tomorrow.

Thank you for your TIPs. tomorrow mayby it will work correct - with some magic :D
 
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jr9

jr9

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Dec 6, 2017
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All CPUz does is read your SPD data. CPUz is wrong in this case. BIOS is the ultimate authority when it comes to your system configuration. If BIOS says you only have 24GB then that's what the system can use.

The motherboard definitely seems a bit off.
 
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dusan.chlud

Feb 23, 2018
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well, CPU and socket looks fine. I tighten water cooler with precision - no difference. Still showing 4 slots in use, but 24GB memory

In my opinion, motherboard is bad.

but still - why only 2 DIMMs not work, but more is fine.. ?
 
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jr9

jr9

Estimable
Dec 6, 2017
2,212
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3,960
There is no ascertainable reason for it that I can see. If it doesn't work properly with two DIMMs then that generally indicates an issue with the motherboard or one of the RAM modules. It should be able to work with two DIMMs.
 
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