Kreisen 3 8 6 X / X E - Manual (Page 84)

this command will still change the system prompt to B>, even
though there is only one physical drive present.
The BIOS “pretends” there are two disk drives present. It
routes all commands intended for the B drive back to the A
drive.
This feature is intended to allow owners of single drive systems
to use application software designed for dual drive systems.
Copying Your MS-DOS Diskettes
The first important task you must complete with your new
system is to make a “backup” copy of your MS-DOS diskettes.
To do this, you will need seven blank diskettes. It is a good
idea to prepare seven diskette labels at this time. Write the
following on those diskette labels, using a felt tipped pen:
MS-DOS MAIN SYSTEM DISKETTE
BACKUP COPY (Version #)
Write down the MS-DOS version number on each diskette
labels. This will avoid confusion later if you upgrade your
operating system to a new version. As you finish copying and
checking each MS-DOS master diskette, peel the correct label
off of the backing paper and place it on the upper left-hand
side of the front face of the new diskette.
The following procedures will show you how to make backup
copies of your MS-DOS master diskettes on both single and
dualdrive systems.
4-12 Using MS-DOS With Your Computer