Types of SCSI Signals

There are three distinct types of SCSI signals:

1. Single Ended (SE)
   Most SCSI devices use "normal" SE signaling, which limits the maximum length of a SCSI bus to 1.5m (4.9ft). This includes most 50-pin (Narrow) SCSI devices such as scanners and Zip drives.



2. High Voltage Differential (HVD) (also known as "Differential")
   A Differential SCSI system provides reliable signaling in high noise environments over a long bus length (up to 25m [82ft]). HVD hardware cannot be mixed with other SCSI signal types. A Differential bus requires Differential terminators.



3. Low Voltage Differential (LVD)
   A typical multimode LVD/SE SCSI system provides a moderately long bus length (up to 12m [39ft]) and downward compatibility with SE hardware. LVD-rated equipment is required for "Ultra" SCSI standards.