Low Voltage Differential ( LVD) was first introduced in SCSI-3. This is also referred to as Ultra 2 or Fast-40 SCSI. A lower logic level voltage of 3 volts instead of 5 volts is used, and it is not directly compatible with the "old" differential (HVD) SCSI. SCSI data throughput is again doubled to 40 Mega-transfers/sec. Cables are 12 m (40 ft) in length. Cables of up to 25 m (82 ft) are used in Single initiator-single target applications.
By connecting one single-ended peripheral to a multimode LVD bus results in the entire bus getting switched on to the single-ended mode with the single-ended limitations on data throughput as well as the cable length.
This provides a bus burst data rate of 80 Mbytes/sec. The other features include provision of differential data integrity, extending the SCSI bus cable lengths to 25 meters (12 meters with 16 devices) and also provision of easy system configuration for up to 16 devices. This is in fact a huge increase from the Ultra SCSI single-ended cable restrictions of 3 meters and maximum burst transfer rates of 40 Mbytes/sec.
