32-bit pointers can't possibly address more then 2**32 bits of memory (bytes 0..((2**32)-1)). Perhaps, by some funky technique (not so funky, really), HP-UX manages to make almost all of that 4GB available to user processes. If you want more then 4GB of memory space, you have to use 64 bit pointers (or at least greater then 32-bit pointers -- 32-bit intel chips can use 36 bit pointers through PXE36 in some circumstances, with lots of extra work, whcih I don't think perl even supports -- so it's a choice of 32-bit for 4 GiB, or 64-bit for up to 16,777,216 TiB. Since the OP wants more then 4GB, 64 bit it is.