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Table Of Contents  CertiGuide to A+ (Core Hardware)
 9  Chapter 0101:  SCSI

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III  What is SCSI?
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Logical Unit Numbers (LUNs)
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IV  SCSI IDs

As was revealed in the words above, multiple SCSI devices may reside on one bus. This potentially presents a challenge for who's who in the digital zoo. This issue was eliminated by the use of SCSI ID. The ID is a simple numbering system, starting with zero.

SCSI ID 0

By default, SCSI ID 0 is used for the drive containing an Operating System.


A person installing a SCSI device can make a choice of what SCSI ID the drive will use. The most common method of setting the SCSI ID on a drive is by the use of jumpers.

If we refer back to the discussion of binary math in Chapter 0000, we note that this is how most SCSI drives have their ID set:

  • All jumpers off on the ID block give the drive the ID of zero.

  • Putting a jumper on the first pin set creates a SCSI ID of 1.

  • Putting a second jumper on, right next to the first jumper gives a SCSI ID of 3 (2+1).

  • Jumpering three pin sets yields 7 (4+2+1).

Review the SCSI table for an expression of this idea. Note that depending on the drive manufacturer, this table may be reversed.

Table 12: SCSI ID Jumper Settings

SCSI ID

Jumper Settings

0

off / off / off

1

off / off / on

2

off / on / off

3

off / on / on

4

on/ off / off

5

on / off / on

6

on / on / off

7

on/ on / on


SCSI ID 7

By default, SCSI ID 7 is used by the SCSI controller card.


Unique ID

Each SCSI device on a single bus must have a unique ID.


Quick navigation to subsections and regular topics in this section



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III  What is SCSI?
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Logical Unit Numbers (LUNs)
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