Ultra320 SCSI is the latest implemented version of the parallel SCSI-3 standard. It uses a parallel bus, 16 bits wide, running at 160MHz, which makes it able to transfer data at 320MBytes/second. Ultra320 SCSI exclusively uses low voltage differential signaling, which allows cable runs of up to 11 meters.

Ultra320 buses can accommodate lower-speed devices, and in some cases devices at multiple speeds can coexist on the same bus without slowing the entire bus down. Instead, the devices disconnect from the bus when not actively sending or receiving data, allowing the bus to operate at the best possible speed for each device. The one constraint, however, is that if any device on the bus uses single-ended signaling, the entire bus must degrade to single-ended mode.

Ultra320 SCSI is almost exclusively used for hard disks and RAID cages, as its high speed and attendant high manufacturing costs make little sense for other, slower devices.

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