The original SCSI specification allowed up to eight SCSI devices, including the controller, to connect to a single 8-bit SCSI bus. Wide (16-bit) SCSI bus-ses support up to fifteen devices and one controller per bus. All SCSI devices, including the controller, must be assigned a unique numeric identi-fier. These SCSI Ids can be any number from 0 - 7 or, for Wide SCSI devices, 0 - 15. Most SCSI controllers have their ID set to 7 by default.
The IDs 8 - 15 always have a lower priority during arbitration than 8-bit de-vices; this allows 8-bit devices, which do not recognize IDs 8 - 15 to coexist on a SCSI bus with Wide SCSI devices, which may be assigned those IDs. When controlling 8-bit devices, a Wide SCSI controller cannot be assigned an ID greater than 7 because 8-bit devices would not be able to recognize the controller.
Most narrow SCSI 8-bit devices have 3 jumpers for setting the SCSI ID, while wide ones have 4 jumpers. The MSB is the highest value bit; the LSB is the lowest value bit. The most significant bit (MSB) may start on the left or the right; Table 22 shows them from LSB to MSB order going left to right. The jumpers may also be numbered differently entirely (i.e. not 0, 1, 2, 3). In the table, a 0 or 1 denotes jumper off or on, respectively.
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