The memory controllers and MMU’s don’t support 64 bits of physical address space. Right now, I’m using a Macbook Pro with an Intel Core 2 Duo. While the OS and CPU support 64 bit virtual addresses, the physical address space supported is 40 bits, and the memory architecture tops out at 4GB.
Interesting. We have servers with 16 or more DIMM slots, each capable of supporting 4GB DIMMs.........hmmmmm.......running Windows.......hmmmmm..........