Alan, I would assume that if you need that 64 bit addressing (not 64 bit arithmetic, which has been around a long time), you want to use a LOT of memory.
Not necessarily. It may be that you want your Linux processes to have 64 bit linear address space so that they can map files with low density in their address space and have Linux bring in portions that the process needs to see.
One could imagine such a process being sufficiently more efficient to make up for the higher base cost of running 64-bit Linux.
Rob
