Additionally, there is the SCSI connector and transport, which is not present on the drives themselves, but is used to connect devices using TCP/IP networks. The drives themselves would use one of the other three connector types.



Note that a SCSI target device (which can be called a "physical unit") is often divided into smaller "logical units." For example, a high-end disk subsystem may be a single SCSI device but contain dozens of individual disk drives, each of which is a logical unit. Further, a RAID array may be a single SCSI device, but may contain many logical units, each of which is a "virtual" disk—a stripe set or mirror set constructed from portions of real disk drives. The SCSI ID, WWN, etc. in this case identifies the whole subsystem, and a second number, the logical unit number (LUN) identifies a disk device (real or virtual) within the subsystem.



The Centronics 50 connector has 50 pins arranged in two rows one on top of the other. The top row has 25 pins and the lower row has 25 pins. This connector is typically used in SCSI-1 applications such as older scanners, controllers, and external SCSI device cases. See our Available Centronics 50 Cables



The SCSI ID of a device in a drive enclosure that has a backplane is set either by jumpers or by the slot in the enclosure the device is installed into, depending on the model of the enclosure. In the latter case, each slot on the enclosure's back plane delivers control signals to the drive to select a unique SCSI ID. A SCSI enclosure without a back plane often has a switch for each drive to choose the drive's SCSI ID. The enclosure is packaged with connectors that must be plugged into the drive where the jumpers are typically located; the switch emulates the necessary jumpers. While there is no standard that makes this work, drive designers typically set up their jumper headers in a consistent format that matches the way that these switches implement.