There are two slightly differing meanings of the term "hot swapping". It may refer only to the ability to add or remove hardware without powering down the system, while the system software may have to be notified by the user of the event in order to cope with it. Examples include RS-232 and lower-end SCSI devices. This is sometimes called cold plugging. However, if the system can detect and respond to addition or removal of hardware, it is referred to as "true hot plugging". Examples include USB, FireWire and higher-end SCSI devices.