I have 2 no of 1GB DDR2 533FSB RAM installed on my Gigabyte G45GMS2 motherboard Now when I am going to install one 2GB DDR2 667FSB RAM it is showing only 3GB inside BIOS and also on my Windows 7 64bit OS here is no RAM remap setting in BIOS I have tried load optimized default settingI've just installed my windows 10 and since it was running slow on a 2gb ram, I decided to buy a 4gb stick on my 32bit system Long story short, it only shows 22gb usable 768mb(or something close to that figure) is reserved for the (Memory Hole remapping) motherboard address limitation not a windows fault you cant use 4 gb of ram on 32 bit OS, you wil need 64bit OS windows will only show between 3Gb and 35Gb and wont be able to make use of the full amount RAM possible you don't have memory remapping enabled in your bios Dell Inspiron 15 Intel Core 2 Duo T5750 2 0ghz 3gb Ram 15 4 Display Win Xp Windows xp 4gb ram only shows 3gb