"Tim Anderson" wrote in message ...
"Mxsmanic" wrote in message
...
Rick writes:

Looks like PCI Express is a staggering waste of memory space.

Yes, PCI Express is the main guilty party here.

But *why* does this address space have to be in the first 4GB?

To maintain compatibility with OS's that are limited to 4GB.
I came across this note in one of Intel's server motherboard
manuals (which supports up to 8GB):
ftp://download.intel.com/support/mot.../sp2gp2tps.pdf

Note: Memory between 4GB and 4GB minus 512MB will not
be accessible for use by the operating system and may be lost
to the user, because this area is reserved for BIOS, APIC
configuration space, PCI adapter interface, and virtual video
memory space. This means that if 4GB of memory is installed,
3.5GB of this memory is usable. The chipset should allow the
remapping of unused memory above the 4GB address, but
this memory may not be accessible to an operating system that
has a 4GB memory limit.