And z/VM has managed cases like this forever. If you want to learn more, suggest you go to some z/VM sessions at SHARE. Lots of folks there who can speak knowledgably about this.
In case this helps, here's a simplified version of how it works: there are segment and page tables. These indicate what pages exist and where (in-memory, on backing store, not at all), and what segments (1MB? 16MB these days? I forget! Been too long!)-bigger "chunks" of memory-exist. Those can be sparse as well (since 2**64 pages would itself take a lot of memory to describe-let's see, if a PTE (Page Table Entry) was just 4 bytes (probably optimistic), then 2**64 bytes of memory would take 2**(64-12+4)=2**56 bits of memory just to describe, if I've done the math right. That would be a lot. Does this help? .phsiii ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
