Mobo only sees 3.4 of 4gb of ram

Dec 1, 2017
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My motherboard only sees 3.4gb of the 4gb installed, motherboard is a gigabyte ga-73vm-s2 cpu is an Intel core 2 quad q6600 ram is 2x2gb ddr2 800, I do a lot of refurbs on older systems, give them upgrades and sell them for cheap, but I can't sell this one if there is something wrong with it, I've been all through the bios, and have disabled the onboard graphics, I've messed with the memory settings, but can't get it to see the full 4gb, I've also used different ram, and the same result, any help would be greatly appreciated.
 
Are you running a 32 or 64 bit OS? Because a 32 bit OS has do address the video memory as part of the 4GB maximum memory pool as well. So if your Video card has 512 MB of video memory that could be the reason.

Edit: Could be onboard video eating some memory too, though 512 seems excessive for onboard video of that timeframe.