Small computer systems interface. A very widely used high data rate general purpose parallel interface. A maximum of eight devices can be connected to one bus, for example a controller, and up to seven disks or devices of different sorts, Winchester disks, optical disks, tape drives, etc., and may be shared between several computers. SCSI specifies a cabling standard (50-way), a protocol for sending and receiving commands and their format. It is intended as a device-independent interface so the host computer needs no details about the peripherals it controls. But with two versions (single ended and balanced), two types of connectors and numerous variations in the level of implementation of the interface, SCSI devices cannot "plug and play" on a computer with which they have not been tested. Also, with total bus cabling for the popular single ended configuration limited to 18 feet (6 meters), all devices must be close. SCSI is popular and has continued development over a number of years resulting in the following range of maximum transfer rates: Standard SCSI: 5 Mbps (max.) Fast SCSI: 10 Mbps (max.) Ultra SCSI: 20 Mbps (max.) For each of these there is the 8-bit normal "narrow" bus (1 byte per transfer) or the 16-bit Wide bus (2 bytes per transfer), so Wide Ultra SCSI could transfer data at a maximum rate of 40 Mbps. Note that these are peak rates. Continuous rates will be considerably less. Also, achieving this will depend on the performance of the connected device.