Wikipedia
Hot swapping (frequently inaccurately called hot plugging) is replacing or adding components without stopping or shutting down the system With the appropriate software installed on the computer, a user can plug and unplug such components without rebooting Specifically, hot swapping describes inserting and/or removing components without interruption to the system A well-known example of this hot swap functionality is the Universal Serial Bus (USB) that allows users to add or remove peripheral components such as a mouse, keyboard, printer, or portable hard drive depending upon the supplier such devices are characterized as hot-swappable or hot-pluggable Hot plugging on the other hand describes only the addition of components that would expand the system without significant interruption to the system
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