Hemos from the hey-now-get-yer-port-on dept.
axehind writes "In this Byte.com article, Dr Moshe Bar explains some of the differences between IA32 and IA64. He also explains some things to watch out for when porting applications to the IA64 architecture."
It is masked but always present.
I don't know who built to it.
It came before the first kernel.