IBM Dock I - page 125

You have completed the setup for starting up the operating system from
the additional hard disk installed in to the Dock I. When you turn on the
computer attached to the Dock I the next time, the operating system on the
additional hard disk will start up.
When the Computer Is Removed
Whenever you remove the computer from the Dock I and turn
on the computer, the operating system on the hard disk drive of
the computer starts up. Error code I999 3 1 is displayed to
indicate that the bootable additional hard disk is not present.
You can ignore this error code.
Appendix A. Starting up the OS from the Dock I A-7
Title: C74AMST CreationDate: 06/23/93 17:09:07