Ultra SCSI (or SCSI-3), is the latest of the ever-improving SCSI standards, and is the cable of choice for such peripherals as the Iomega Zip Drive. It includes specifications for a single-ended as well as a differential bus style. The single-ended is similar to Fast SCSI-2, except it accommodates addressing up to 32 devices over a 16-bit single cable bus. This new style also increases data throughput up to 20 Mbps in single-ended applications. Single-ended SCSI-3 is limited to 4 devices over 3 meters or 8 devices over 1.5 meters. Differential SCSI refers to a bus configuration using two wires per signal, with the signal being derived by the voltage difference between the two wires.