My understanding is that there's still VM, but it uses a separate buffer (on-chip memory map) containing a list of segments that map each part of the process' m

My understanding is that there's still VM, but it uses a separate buffer (on-chip memory map) containing a list of segments that map each part of the process' memory to a physical address (virt->physical offset + length), rather than a multi-tiered paging structure. The advantage is quick virtual -> physical address translation and less space used for them vs page tables, but the downside, as you point out, is what to do when a process exceeds it's initial heap or stack segment. In this case, I think the Forwardcom solution is to add another entry in the memory map for the next 2*n bytes of heap space.