Apple PowerBook Duo Dock (including Duo Dock Plus) - Manual (Page 17)

Hard disks
The PowerBook Duo starts up from its internal hard disk automatically. If
you have a hard disk installed in or connected to your Duo Dock, that disk’s
icon also appears when you start up.
You may prefer to start up from the Duo Dock’s hard disk when the
PowerBook Duo is docked. If so, use system software version 7.1 or later to
install a System Folder on that disk, and select it in the Startup Disk control
panel. See the instructions on installing system software in the
documentation that came with your PowerBook.
If you start up from the Duo Dock’s hard disk, the preferences selected on
that disk override those selected on your PowerBook Duo. When you use the
PowerBook away from the dock, the PowerBook uses the preferences
associated with its own hard disk.
Startup disk surprise? If you select the hard disk in the Duo Dock as your
startup disk, your PowerBook Duo will also start up from the internal hard
disk of any other Duo Dock you use. (This is because all Duo Dock internal
hard disks have the SCSI ID number 1.)
SCSI devices
If you have a hard disk installed in your Duo Dock, you can chain up to five
additional SCSI devices to your PowerBook Duo System. If you do not have a
hard disk installed in your Duo Dock, you can chain up to six devices.
11 Using the PowerBook Duo Dock