A stand-alone magnetic disk, optical disc or solid state drive that plugs into the computer typically via USB, although eSATA and FireWire are also used. External drives are designed for portable and stationary use (see portable hard drive). See SATA, FireWire and solid state. External Drives Used to Be SCSI In the 1990s, the term occasionally referred to external SCSI disks and tapes, which plugged into the SCSI controller in the computer. Contrast with internal drive. See USB drive and SCSI.