ultra SCSI (USCSI)
Ultra-SCSI is a variant of Small ComputerSystem Interface (SCSI) with higher throughput rates. There are different Ultra-SCSI versions: Ultra-SCSI, Ultra-2-SCSI, Ultra-3-SCSI or Ultra160-SCSI and Ultra320-SCSI.
Ultra-SCSI offers a transfer rate of 20 megatransfers per second( MT/s) with SCSI bus lengths of up to 1.5 m with single-ended termination and up to 25 m with differential signals. Specifications include bus widths of 8 bits and 16 bits. Transfer rates of 20 MB/s are achieved via the narrower 8-bit widedata bus, and 40 MB/s via Wide-SCSI with 16-bit bus width.
In theUltra-2-SCSI version, the transfer rate is 40 megatransfers per second with a bus length of up to 12 m in unbalanced transmission with Low Voltage Differential( LVD). In the second mode with higher symmetrical voltage, the bus length is up to 25 m. Similarly, Ultra-2-SCSI distinguishes between two bus widths with 8 bits and 16 bits. With the narrower bus width, transfer rates of 40 MB/s are achieved at a clock frequency of 40 MHz, and 80 MB/s with the wider one. Ultra-2-SCSI requires special data cables in which the ground line and the current-carrying line are twisted together. These cables must be terminated with an active termination at the end of the cable because Ultra-2 SCSI devices can no longer be terminated directly.
In the Ultra-3-SCSI or Ultra160-SCSI version, the transfer rate is 160 megatransfers per second with a bus length of up to 12 m with unbalanced transmission via the LVD bus. Ultra-3-SCSI specifies only a 16-bit wide SCSI bus over which data transfer rates of 160 MB/s can be transmitted, but has cyclic block checking(CRC).
The most powerful SCSI version is Ultra320-SCSI with a transfer rate of 320 MB/s. The bus width is 16 bits, the cable length is 12 m and up to 12 drives and other peripherals can be connected. With this SCSSI version, both edges of the clock signal are used for data transfer.