Why does a 32bit domU (Xen guest VM) use less RAM than a 64bit?
Notes: The same software complied for a different arch(AMD64 vs. 686). Obviously this is Linux or BSD or something easily ported. Maybe this is also a good one for SO.
I've read this is so. I can guess why, but I'd like to hear everyone's comments.
Under the same workload, a 32-bit system will always use less memory than a 64-bit one, mainly due to two reasons: the bigger size of executables, pointers, variables etc., and the additional kernel overhead of managing a bigger address space.
This of course doesn't happen only to virtual machines, but to physical systems too.