High Voltage Differential (HVD) is the "old" differential SCSI that uses higher voltage levels which were originally defined in SCSI-2, offering 25 meter (82 ft) cable length. Though HVD and LVD SCSI are not directly compatible, they can be interconnected using a SCSI expander, which is known as an LVD to HVD Converter.
Signaling
HVD uses "Differential" signaling as against "Single Ended" signaling which makes HVD and SE completely incompatible with each other. HVD to SE converters are usually very costly.
Pinout
A pinout called "Straight Through" is used by all SCSI, which means that any SCSI cable will work (the pinout will match) as long as the connectors are the same on both ends.
