[mhh__]

256 bits in the case of a worldwide mega-computer would be such a huge departure from current architectures and more importantly latency-numbers that we can barely even speculate about it.

It may be of note that hypothetically one can have a soft-ISA 128 bit virtual address (a particularly virtual virtual address) which is JITed down into a narrower physical address by the operating system. This is as far as I'm aware how IBM i works.

[arthur2e5]

For what is worth, 256 / log2(10) is around 77, while the observable universe is estimated to have anywhere from 10^78 to 10^82 atoms. An 256-bit address space, if fully utilized, would produce Asimov’s AC from The Last Question.

More realistically though, we would throw away at least half that length like how we are handing out /64 blocks to everyone on IPv6.