High voltage differentialHigh voltage differential stands for an electrical signalling system using high voltage, as in opposite to low voltage differential signalling (see LVD). In the computer arena, "high voltage" normally stands for 5 volts or more. Such circuitry normally allows longer cable length than so called single ended versions. This is because the signal on the wires is not received as a delta of a signal wire to ground, but as the difference between pairs of wires not related to ground (hence the term "differential"). Since any distortion to the signals coming from external sources are likely to influence the pairs by an equal amount, the maximum cable length is increased when related to single ended circuitry.
SCSI equipment for example allows a maximum total cable length of 25 meters using HVD, while single ended SCSI allows a maximum cable length of 1.5 to 6 meters, depending on bus speed. Note that LVD versions of SCSI allow less than 25m cable length not because of the lower voltage, but because these SCSI standards allow much higher speeds than the older HVD SCSI.