Design Notes for 1.4  - 

12/25/2011 DWG - Logical Unit enhancement for block drivers

The previous version implemented Logical Unit functionality
by poking an offset word into a private data structure in
PPIDE_DATA.ASM.

In order to make the Logical Unit functionality more generic,
Wayne suggested adding the appropriate data items to the end
of the Disk Parameter Header data structure (because there is
one each for each drive).

The added items consist of a Logical Unit enhancement signature
which is two bytes "LU", and several subsequent items including
a default slice number and status.