The virtual addresses add up to about 6 GB. The resident memory is about 2 GB.

If a program allocates a 5 GB array its virtual address space utilization instantly increases by 5 GB because addresses must be assigned to all 5 GB. But the OS is not stupid enough to instantly dedicate 5GB of physical memory to that array. As the program actually uses the array the OS will allocate memory page by page.

And think about a program like vim. It's a huge program with many features but most of us don't use them all. As we use features in vim, if the code is already in core, fine. Otherwise a page fault is generated and a page is read in. vim page-faults just enough stuff into core to do what we want. The rest stays on disk.