If you locate the disk ID's in IODFAULT.PUB.SYS, you will see that all Wide/Differential SCSI disks have the same parameters. As long as you do not configure a Single-Ended SCSI disk where you really have a Wide/Differential SCSI disk, or vice versa, you can use any ID in that group. What you see is normally a result of the product number being used as the device ID (where valid in IODFAULT), while the device really has a different internal ID. Note to watch out for ambiguous disk ID's like ST34573WC that can be a Single-Ended or Wide/Differential device.