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What do the terms Single Ended and Differential mean?
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Single-Ended and Differential (sometimes referred to as HVD, or High Voltage Differential) refers to the number of data lines vs. ground lines on a given SCSI device.
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On a Single-Ended device, one line defines one bit. A high (or negated) signal denotes a logical zero, a low (or asserted) signal denotes a logical one. In a Differential device, two lines, instead of one are used to define a bit. The information is defined as the difference between the two signals (which are referred simply as + and - ) and not just the voltage level of a single line. Since the differential between two lines is used, (hence the name) this type of SCSI is more robust than Single-Ended and can travel longer distances without noticeable signal degradation. Though both Differential and Single-Ended devices use the same connectors, they are electrically different and require different types of host adapters. High Voltage Differential devices will not work with Single-Ended host adapters and vice-versa.
Differential (High Voltage Differential) drives and LVD (Low Voltage Differential) drives differ from each other. The most notable difference is that LVD drives can work on Single Ended host adapter, and likewise, an LVD host adapter can work with Single Ended drives, though mixing Single Ended devices with LVD device on the same cable will result in the entire cable operating in Single Ended mode.
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