Question : Problem: Windows see 4GB - Bios just 2GB

Hello,
I have Windows Vista Ultimate 64-Bit SP1 OS with all the updates.
I've just put 2 memory sticks 2GB each and got the following problem:
Bios only recognize 2GB while Windows (In some parts) is saying that I have 4GB. But not everywhere.
When I go to the system properties, It says 4GB. When I'm looking at the sidebar, It says 2GB.
In bios, It says 2GB. My 2 previous memory sticks were 1GB each and were apparently high-density (128X8)
Those 2 sticks are apparently 128x16 (8 on each side) which is apparently following the standards (I might be wrong here)
Does that mean that my mainboard doesn't suport 2GB modules?
Thanks in advance!

Answer : Problem: Windows see 4GB - Bios just 2GB

Most of the time motherboards / system will work with the modules they were designed for and there is some flexibility regarding speed, memory timings, etc., but in some instances boards can be very picky about the types of RAM that will work in them.  Below is a list of the Fully Qualified Modules supported by your motherboard:

http://www.gigabyte.com.tw/FileList/MemorySupport/motherboard_memory_ga-g31m-s2l.pdf

There is only one DDR2 800 MHz 2 GB stick listed as qualified on this list, outside of these modules Gigabyte makes no guarantee other modules will work.  The board may also be defaulting in the wrong voltage or timing settings.  The specs on that Micron 2 GB module from the compatibility list are a voltage of 1.8 and CL of 6:
http://www.micron.com/products/partdetail?part=MT16HTF25664AY-800

If you are using 2 GB modules from a different manufacturer make sure they support that same voltage and timing as the micron model and then make sure your motherboard is set for that same memory voltage and timing, you should be able to change these settings in the CMOS settings.

Good luck!