The SCSI ID number is 0 for the optional internal 20MB SCSI hard disk
available in the Macintosh SE. The CPU uses ID number 7, so additional
SCSI devices connected to the Macintosh SE may use ID numbers 1 through 6.
You must be able to set numbers 1 through 6 on any more SCSI devices you
connect to a Macintosh SE with the optional 20MB SCSI internal hard disk.
The internal hard disk's ID number, set in firmware, can't be changed.