Comment by hinkley

I believe the new garbage collector for the JVM colors pointers in a way they are not scrubbed before use; they memory (re-)map into multiple regions to implement read and write barriers.

Some very old distributed systems used 64 bit pointers where the upper bits told you what machine the data was on.

And we have Intel putting SSD card in DIMM slots. I expect there are semantics attached to those address ranges as well.

I dunno where we are after Spectre, but one of the microkernel architectures got its IPC speed by packing most processes into a couple of address spaces, only with different read write access. On preemption the TLB wasn’t invalidated (about half the cost), just modified.

These are the sorts of tricks you do when your address space is bigger than you will ever need. I expect to see more of this as time goes on. And if we ever see 128 bit pointers, expect crazy stuff like this to be de rigeur.