Hot swapping an hot plugging are terms used to separately describe the functions of replacing system components; hot swapping describes changing components like fans and power supplies which do not interact with the system software, while hot plugging describes changing or adding components like hard drives which do interact with the operating system. Both terms describe the ability to remove and replace components of a machine, usually a computer, while it is operating. For hot swapping once the appropriate software is installed on the computer, a user can plug and unplug the component without rebooting. A well-known example of this functionality is the Universal Serial Bus (USB) that allows users to add or remove peripheral components such as a mouse, keyboard, or printer. It usually requires more sophisticated software and hardware than does plug-and-play.