ARCHIVED: What is a swap file?

A swap file allows an operating system to use hard disk space to simulate extra memory. When the system runs low on memory, it swaps a section of RAM that an idle program is using onto the hard disk to free up memory for other programs. Then when you go back to the swapped out program, it changes places with another program in RAM. This causes a large amount of hard disk reading and writing that slows down your computer considerably.

This combination of RAM and swap files is known as virtual memory. The use of virtual memory allows your computer to run more programs than it could run in RAM alone.

The way swap files are implemented depends on the operating system. Some operating systems, like Windows, can be configured to use temporary swap files that they create when necessary. The disk space is then released when it is no longer needed. Other operating systems, like Linux and Unix, set aside a permanent swap space that reserves a certain portion of your hard disk.

Permanent swap files take a contiguous section of your hard disk while some temporary swap files can use fragmented hard disk space. This means that using a permanent swap file will usually be faster than using a temporary one. Temporary swap files are more useful if you are low on disk space because they don't permanently reserve part of your hard disk.