Swap file

A swap file, also referred to as a memory page, is used by a program or, more often, the operating system as temporary swap space to store the contents of virtual memory on a storage drive when not enough physical memory is available.

Description
A swap file is usually allocated as a contiguous block of a drive space to reduce access time. In the meantime, the drive space used for a swap file can not be used for other purposes. Swap file performance was once considered slow due to the latency of reading and writing to a hard drive, but has improved with the adoption of solid-state drives (SSDs). However, some users have expressed concern that swap file activity would reduce the life expectancy of SSDs.

History
In 1990, Adobe Photoshop became one of the first programs to introduce the use of a swap file (called "scratch disk"), when Apple Computer's own System 6 had not yet implemented virtual memory. Under Microsoft Windows, swap files are recommended not to exceed three times the available RAM and are usually 150 percent of the RAM size.