Editing Memory paging (section)

===Main memory the same size as virtual memory===
A computer with true ''n''-bit addressing may have 2{{Sup|''n''}} addressable units of RAM installed. An example is a 32-bit [[x86]] processor with 4&nbsp;[[Gigabyte|GB]] and without [[Physical Address Extension]] (PAE). In this case, the processor is able to address all the RAM installed and no more.

However, even in this case, paging can be used to support more virtual memory than physical memory. For instance, many programs may be running concurrently. Together, they may require more physical memory than can be installed on the system, but not all of it will have to be in RAM at once. A paging system makes efficient decisions on which memory to relegate to secondary storage, leading to the best use of the installed RAM.

In addition the operating system may provide services to programs that envision a larger memory, such as files that can grow beyond the limit of installed RAM.
Not all of the file can be concurrently mapped into the address space of a process, but the operating system might allow regions of the file to be mapped into the address space, and unmapped if another region needs to be mapped in.