Terminology
Historically, paging sometimes referred to a memory allocation scheme that used fixed-length pages as opposed to variable-length segments, without implicit suggestion that virtual memory techniques were employed at all or that those pages were transferred to disk. Such usage is rare today.
Some modern systems use the term swapping along with paging. Historically, swapping referred to moving from/to secondary storage a whole program at a time, in a scheme known as roll-in/roll-out. In the 1960s, after the concept of virtual memory was introduced—in two variants, either using segments or pages—the term swapping was applied to moving, respectively, either segments or pages, between disk and memory. Today with the virtual memory mostly based on pages, not segments, swapping became a fairly close synonym of paging, although with one difference.
In systems that support memory-mapped files, when a page fault occurs, a page may be then transferred to or from any ordinary disk file, not necessarily a dedicated space. Page in is transferring a page from the disk to RAM. Page out is transferring a page from RAM to the disk. Swap in and out only refer to transferring pages between RAM and dedicated swap space or swap file or scratch disk space, and not any other place on disk.
On Windows NT based systems, dedicated swap space is known as a page file and paging/swapping are often used interchangeably.
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