I have an Asus z8PE-D18 motherboard and two Intel, xeon, E5520 processors installed. I tried Suse 11.1, RedHat 5.4, and ran System rescue. All seem to run perfectly, but /proc/cpuinfo on all software reports that there are 16 processors installed. The E5520 is a 4 core processor, why does Linux report there are 16 processors?
because they are hyper-threaded? 4 physical cores + 4 virtual (HT) cores 
Thanks, I believe that is the reason.