UD -- UNLOCK DIRECTORY By WESLEY HOWE
     UD is a 108-byte Assembly-language program to unlock the current
Directory and set it to the root of the filing system (the boot disk). UD
was written to overcome the problem where the CD command attaches to a disk,
rather than a device.
     It is most useful on single-drive systems, where swapping disks can
become a problem. For example, if you use CD on a single drive system even
once, you must use it each time you change the disk in DF0: or the system
will keep asking for the old disk by name.
     On two-drive systems, it is often more convenient to move the bootdisk
to DF1: and change disks in DF0:. If you use CD to inspect a directory, then
use CD DF0: to get out, you will need to use CD DF0: each time you want to
change the disk in DF0:. I find that cumbersome and inconvenient.
     Enter UD. After using the CD command, UD will set the current directory
to the disk drive DF0:, not the volume in DF0:. This is the way the system
defines the current directory after a reboot prior to ever using the CD
command.