A data channel that transfers digital data in a serial fashion: one bit after the other over one wire or fiber. Serial interfaces may have multiple lines, but only one line is used for data. The other lines are used for control. On earlier PCs, the serial port was a serial interface for attaching modems and data acquisition terminals, and sometimes mice. See serial port. Common Desktop Computer Serial Interfaces USB is widely used for attaching myriad peripheral devices. Popular in the Apple world, FireWire (IEEE 1394) is used for video transfer. Serial ATA (SATA) is the popular hard drive interface. Contrast with parallel interface. See USB, FireWire and SATA.