Quote Originally Posted by movieman View Post
If the extra memory isn't remapped, it will be hidden by the PCI memory mapping.

That said, I guess the OS could do remapping itself, but by the time it boots that may be too late.
I've made the test yesterday, disabling the memory remapping in the bios. That leads to 3.3Gb usable only, even with the 64Gb PAE kernel.

In fact, as soon as the PC starts, bios detects only 3.3Gb without memory remapping (startup bios display), and I presume the memory lost can't be recovered by the OS in a later time.