SCSI cables are available in two distinct varieties:
External cables
External cables are often used to connect SCSI devices that do not reside inside the PC. They are totally different in their construction mainly because the external environment is much more prone to risk of the data getting corrupted which means external cables are to be designed to protect the data traveling on the cable.
Internal cables
Internal cables connect SCSI devices installed within the PC. The chassis or metal case of the computer, shields the components inside from most of the electromagnetic and radio frequency noise and interference from the "outside world".
