Hot swapping (or Hotplugging) is the ability to remove and replace components of a machine, usually a computer, while it is operating. Once the appropriate Software is installed on the computer, one can plug and unplug the device without booting. An example of this is the Universal Serial Bus (USB), that allows a user to add or remove peripheral devices such as a mouse, keyboard, or printer.

Historically, only expensive systems have this ability as it is very difficult to engineer correctly.

Machines that support hot swap need some ability to detect that a component has been removed. In addition all electrical and mechanical connections need to be designed such that neither the part nor the user can be harmed by removing it. Lastly, other parts in the system must be designed such that the removal of a different part does not harm operation. (Often there is some automatic recovery process.)

Simple implementations often require a component shut down procedure prior to removal. This simplifies implementation, but such devices are not robust in the case of part failure. Modern small computers often have USB and/or FireWire (also known as IEEE 1394) buses that support this simple hot swap. If a device is removed while it is being used, the operations to that device fail and the user is responsible for retrying if necessary. As this action is normally done by end users this is not considered a problem. These hot swap operations are generally used either to move a computer peripheral from one computer to another, or to allow a device to synchronize data with a computer.

Complex implementations may recommend that the part be shut down, but there is sufficient redundancy in the system such that if a part is removed without being shutdown operation continues. In these systems hot swap is normally used for regular maintenance to the computer, or to replace a broken part.

Additionally, there are two slightly differing meanings of the term hot swapping. In some contexts, it refers only to the ability to add or remove hardware without powering down the system, while in other contexts, it refers to the system s ability to autonomously detect when hardware is added or removed. In the former case, one can add or remove hardware without powering down, but the system software may have to be notified of the event in order to use the new hardware. Examples of the former include RS-232, FireWire and lower-end SCSI devices, while examples of the latter include USB, FireWire, PCI Express and higher-end SCSI devices. When comparing these two cases, it is common to only refer to the latter case as true hotplugging, and call the former case coldplugging.

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