Memory >3.5GB not used?

[Don O'Neil]

I just built a new server with an Athlon 64 x2, 4GB Ram and a
Gigabyte/Nvidia motherboard.

When I boot the system up it says on the console that 532888K will be
ignored.

Of course it isn't put in any of the log files. Dmesg shows this:

real memory  = 3724476416 (3551 MB)
avail memory = 3649908736 (3480 MB)

Any reason the extra 1/2 GB isn't showing up or usable? Is there something I
need to specify in the kernel to get to the other 1/2 GB? What if I want to
install more than 4GB? This mobo supports up to 16 GB... Do I need to go to
the AMD64 platform to get >4GB?

I'm running FreeBSD 6.1 i386 SMP kernel.