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SCSI Data Transfer Modes and Feature Sets
The technologies used in SCSI are defined by the formal standards created and maintained by industry groups and standards associations. However, SCSI hardware is usually not sold labeled with the name of the standard whose features it implements. This is probably a good thing; considering the number of different protocols and transfer modes that are covered by both the SCSI-2 and SCSI-3 names, being told a drive is a "SCSI-2 drive" or "SCSI-3 device" doesn't really tell you much of anything at all!
Instead, SCSI devices are usually sold using specific names that define particular "flavors" of SCSI. Each of these is a particular intersection of various important SCSI characteristics, such as bus speed, bus width and signaling type. In most cases new feature sets are created when new transfer modes are created by the adoption of new standards; they are then given cute names by various hardware makers or manufacturers' associations and used to promote the new products. The various feature set names can be hard to understand since some of them are similar to each other despite different-sounding names.
In this section I provide a description of each of the common feature sets used for regular parallel SCSI. For each one I provide the following information in a standardized format:
Next: "Regular" SCSI (SCSI-1)