Hot-plugging

Hot swapping and hot plugging consist in replacing or adding components without stopping or shutting down the system. More specifically, hot swapping describes replacing components without interruption to the system, while hot plugging describes the addition of components that would expand the system without significant interruption to the operation of the system. 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.

Computer components are usually described as cold-pluggable if the computer system must be powered down to add or remove them. The opposite term is hot-pluggable; hot-pluggable components can be added or removed without powering down the computer. Most components in computer systems, such as CPUs and memory, are only cold-pluggable. However it is common for high-end servers and mainframes to feature hotplug capability for other components, such as PCIe and SATA.

The terms hot plug and cold plug can be taken to mean two different things, depending on the context. In a more generic context, hot plug is the ability to add or remove hardware without powering down the system, while cold plug is the inability to do so. In the context of comparing certain hot-pluggable devices, however, hot plug can be taken to mean the ability of the system to autonomously detect the addition or removal of hardware as it occurs, while cold plug can be taken to mean the ability to add or remove devices without powering down or rebooting the system, but the inability of the system to detect these changes, in which case the system operator would have to tell the system software that the change has occurred.

Hot swapping is used whenever it is desirable to change the configuration or repair a working system without interrupting its operation. It may simply be for convenience of avoiding the delay and nuisance of shutting down and then restarting complex equipment or because it is essential for equipment, such as a server, to be continuously active.

...
Wikipedia