The "reserved for hardware" answer is the same one I got when running 32 bit Vista with 4GB a year ago. What is the advantage of using a 64 bit OS with 4Gb ram then? And why are there so many references to win32 when you generate a system health report in Windows 7 64 bit? It looks like this:
Operating System Info
--- or this further down the list ---
root\cimv2:SELECT __Relpath, Name, Caption, Description, DisplayName, PathName, Started, ExitCode, State, ServiceSpecificExitCode FROM Win32_Service
with every available/running windows service listed as a "Win32" service after it.
I upgraded to Windows 7 64 bit (which it reports as OS in other places) from Vista Home Premium 64 bit. Here are machine specs.
Gigabyte GA-P35-DS3L (latest bios)
Core 2 Duo E6600
4GB G-Skill RAM (2x2GB)
HTO CLARO Sound
Intel Gigabit CT NIC
EVGA Nvidia 260 GTX 216 core Video
THERE IS NO MEMORY REMAP OPTION IN MY BIOS