Tim Anderson wrote:
"Rick" wrote in message

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.

Yes, this is helpful. Thanks. So the proper question may be this:
Why don't these 4GB boards remap this memory to make it usable by
64-bit operating systems?

Because it is an unnecessary expense. While there may be uses for
addressing over 4GB to conveniently handle large databases etc.,
there is virtually no real need for that much actual memory.

The function can be efficiently served by virtual memory systems at
little performance cost. About the only area where I can conceive
such real memory to be useful is in high performance video
processing.

--
Some informative links:
news:news.announce.newusers
http://www.geocities.com/nnqweb/
http://www.catb.org/~esr/faqs/smart-questions.html
http://www.caliburn.nl/topposting.html
http://www.netmeister.org/news/learn2quote.html