Some computer devices support chaining, the ability to string multiple devices in a sequence plugged into just one computer port. Often, but not always, such a chain will require some sort of terminator to mark the end. For an example, a SCSI scanner may be plugged into a SCSI CD-ROM drive that is plugged into a SCSI hard drive that is in turn plugged into the main computer. For all these components to work properly, the scanner would also have to have a proper terminator in use. Device chaining has been around a long time, and it is interesting to note that C64/128 serial devices supported it from the very beginning. Today the most common low-cost chainable devices in use support USB while the fastest low-cost chainable devices in use support FireWire.