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Windows (10) and BIOS can see only half of the memory (16gb/32gb) only two slots are active at time

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yuniyhimik

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No he didn't, he said the 2x 4GB sticks showed up normally.

I asked him to throw in 1x 4GB and 1x 8GB per channel, 4 in total. He did, then posted a screenshot of 1x 4GB and 1x 8GB in each channel, slot 1 & 3, the other slots were empty. This means from the 8GB sticks he bought he installed one which is ion fact a 4GB module, or else the 8GB stick he installed doesn't have any usable RAM.

It can't be any other reason because of the way Intel remaps memory on dual channel boards.
When the modules are unequal the size of the smallest density is dual and the leftover from the bigger module is remapped by the board, some hybrid single channel,
I don't know exactly how it's remapped but anyway it's not dual channel.

Another point I should make is that by one incredible coincidence I had a 4GB module go bad during a platform test yesterday, and guess what...Exact same symptoms as OP.
Only I double checked and tried post with each module, surprise...surprise, out of 4x4GB sticks, no post with one of them.

12GB shows up in BIOS main page, but in SPD page it's all there.. OS reports 16GB installed, 12GB usable. Running in single channel.

The OS doesn't have any direct access, it's virtualized.
It reads a chip which describes density size, timings etc, however when it comes to address space the BIOS doesn't assign any, because there isn't any RAM to assign.

To windows it would appear the same as hardware reserved.

I could put up screenshots but tbh I can't be assed......If the OP wants to do his own investigation, that's cool with me.
Well, in fact I did say that old and new memory both act exactly the same.

When I use old memory sticks - they work if they are in the same channel, but if one is in A and another one in B - only 4gb shows up.
There is absolutely no difference in old and new memory handling by the board.

Which means either I have 2 in-a-weird-way-faulty memory kits, or memory isn't the issue. Or maybe my MB just isn't compatible with any decent memory, many years old, or new.
Asus says: it should work no problem with 4 x DIMM, Max. 32GB, DDR3 2400(O.C.)/2200(O.C.)/2133(O.C.)/2000(O.C.)/1866(O.C.)/1800(O.C.)/1600/1333 MHz Non-ECC, Un-buffered Memory Dual Channel Memory Architecture
 

Aquinus

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No he didn't, he said the 2x 4GB sticks showed up normally.
Guess what. He also did just the old memory in A1 + B1 and only 4GB showed up.
Well, in fact I did say that old and new memory both act exactly the same.

When I use old memory sticks - they work if they are in the same channel, but if one is in A and another one in B - only 4gb shows up.
There is absolutely no difference in old and new memory handling by the board.
That sounds to me like a issue with the CPU's IMC or the motherboard.

@yuniyhimik : Have you tried starting the machine with a single DIMM in b1 or b2?
 

squeezehat

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I don't know how the BIOS itself could affect the amount of RAM showing up since RAM is enumerated by chipset.. The BIOS doesn't know how much is actually installed is until then....
BIOS is responsible for querying the ram modules during initialization. BIOS is also responsible for programming the memory controller...
 

jm9k

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I'm having a similar problem with my Asus board. I have a 4x4GB DDR3 1600 kit. Now it only detects 8GB/16GB. The BIOS finds the memory and can read the SPD info for all chips but only shows half the memory. I tried one stick at a time in each slot. Everything works! It just never shows above 8GB as usable. I've tried everything in every thread including the BIOS 4GB remap setting, different speeds, voltages, reseating CPU, resetting the CMOS. I also tried pulling out every single other component, tried 3 different video cards, and a different power supply. Even Memtest86 shows the correct SPD info, but only shows 8GB.

Now here is the weirdest thing, it used to work fine. I first noticed the problem when I moved my motherboard into a new case. My best guess is it is a hardware problem, not a setting problem.
 

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I'm having a similar problem with my Asus board. I have a 4x4GB DDR3 1600 kit. Now it only detects 8GB/16GB. The BIOS finds the memory and can read the SPD info for all chips but only shows half the memory. I tried one stick at a time in each slot. Everything works! It just never shows above 8GB as usable. I've tried everything in every thread including the BIOS 4GB remap setting, different speeds, voltages, reseating CPU, resetting the CMOS. I also tried pulling out every single other component, tried 3 different video cards, and a different power supply. Even Memtest86 shows the correct SPD info, but only shows 8GB.

Now here is the weirdest thing, it used to work fine. I first noticed the problem when I moved my motherboard into a new case. My best guess is it is a hardware problem, not a setting problem.
You should've created your own thread for this if only not to necro a super old thread, it's netiquette and frowned up here, with a big red warning as stated above. But welcome to TPU and maybe start that new thread! ;)

For a quick answer, it is probably a bent pin...and all it takes is the right pin(s)...I had the same issue with a P55i Sabertooth + i5 760 combo, a couple of bent pins and I could only see 4GB of 8GB in Win 7x64 and BIOS.
 
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