Swap File

Techopedia explains Swap File

Introduced to supplement physical PC memory limitations, swap files are still used in operating systems like Windows 7 and Windows Server 2008, as virtual memory is a cheaper alternative to magnetic media. A typical swap file is equal to or larger than the system's total installed physical memory. The exact size is based on the OS and amount of physical memory, as well as applicable personal and/or corporate policies and preferences.

Although swap files provide additional system memory, the data stored in swap files is typically less active or idle because HDD transfer and access speeds are much lower than solid state memory.