Processes on SunOS execute in a 32-bit address space. The OS arranges matters so that each process
thinks it has exclusive access to the entire address space. The illusion is sus-tained by "virtual
memory," which shares access to the machine's physical memory and uses disk to hold data when
memory fills up. Data is continually moved from memory to disk and back again as a process runs.
Memory management hardware translates virtual addresses to physical addresses, and lets a process
run anywhere in the system's real memory. Application programmers only ever see the virtual
addresses, and don't have any way to tell when their process has migrated out to disk and back into
memory again, except by observing elapsed time or looking at system commands like "ps". Figure 7-3
illustrates the virtual memory basics.
Figure 7-3. The Basics of Virtual Memory