I recently brought a motherboard(M5A78LMUSB3) and a ram of 4 GB DDR3 1600(corsair Vengence(CMZ4GX3M1A1600C9))........i paired the ram with my existing 2GB 1333 DDR3 and AMD 2.8 GHz AM3 Sempron 145 Processor........the new ram is not in the QVL list that asus provided........i also have two 320GB HDD........when i installed win 8.1 64 bit i used to get 5.75GB, now i downgraded to win 7 64 bit because of graphics driver os support issue..........and im getting exactly 3.75GB of ram insdead of 5.75GB........Hardware reserved is 2306MB.....and total available is 3838mb........here are the motherboard specs►http://www.asus.com/Motherboards/M5A78LMUSB3/specifications/