I had absolutely no idea which subform to make this thread in so it's in General for now.
I have an old Pentium D PC with an Intel D945GTP motherboard (945G chipset) and according to the Intel specifications, its max memory is 4 GB of DDR2. I upgraded it from 3 to 4GB, without changing any other settings, and it suddenly shows ~512MB as hardware reserved, with 3.5GB usable. The mobo's onboard graphics are disabled since it has a PCI-E video card installed. Running 64-bit Windows 7. Any ideas what this could be?