Z170 Extreme4 where is my RAM

have you checked the memory ranges of all your devices in the Windows device manager (view by resources)? Probably you will see there, why only 2GB are used and which device is registering for the rest of the memory space.

gvenko wrote: Hi. I have strange problem: On this MB I have GEIL memory 16GB(8GBx2) PC4-19200 2400Mhz CL16-16-16-36 EVO POTENZA but I needed to install W7 32bit, so expected windows to see about 4GB RAM. In fact Windows see only 2GB and I don't understand why. The shared memory for graphics is set to 32MB (the lowest possible). The CPU is Intel Skylake i3-6100 and there is Silicon Power S70 SSD 2.5" SATA 240GB disk. Any ideas please?

What UEFI/BIOS version do you have in your board now?

Your GEIL EVO Potenza (this model, GPR432GB2400C15QC, but a 16GB kit?) as an 8GB DIMM is double sided (DS), which should be used in the A1 and B1 slots.

Can you run CPU-Z to check if your memory is running is dual channel mode? This is an example of CPU-Z on an X99 board. On the upper right we can see the number of channels being used, on the upper left we can find the amount of memory being detected:

By chance the win 7 you have....???

Windows 7 Starter x86 does only recognize 2GB

HERE is the MSDN Win7 link that shows usable/available memory limits on the differing Windows 7 editions.