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                                 LADDR UPDATE
                                 Bruce Bonner
                               October 26 1990

On June 11, 1990, Western Digital, Microsoft and other companies jointly
announced the inclusion of SCSI capability in Microsoft OS/2.  The software
package from Microsoft for this is called "LADDR", which stands for "Layered
Device Driver".

SCSI is a double edged sword.  Its biggest advantage is flexibility with many
different types of peripherals.  Its biggest DISadvantage is flexibility
with many different types of peripherals.  The flexibility makes it so SCSI
software solutions need to be very robust so everyone can have the features
and connectivity they need.  Because of this Western Digital strongly
encourages OS/2 SCSI developers to use LADDR.  It is a very complete
software solution that overcomes the inherent problems of connecting SCSI
peripherals into an operating environment.  It does this by using various
software layers to define the variables of host bus adapters (HBAs),
peripherals, and vendor specific features of those peripherals.  Very "thin"
software layers are used to minimize performance impacts.

The beta version of the Microsoft LADDR development kit (LDK) is now
shipping.  LADDR development kits can be obtained from Microsoft by calling
them at (800) 227-6444.

Western Digital has provided Microsoft with our BID module for the 7000-
FASST2 and 7000AX (under the 7000AX name).  We will soon send them BIDs for
our other SCSI HBA products, such as the 7000EX and 7000MX.  When the code
is stable we also will distribute these BIDs on the WD BBS, and will license
the source code to WD OEM customers on request.

LADDR is compatible with OS/2 versions 1.21 and higher (including 1.3), and
is added as an installable driver to this version by the user.  LADDR will
be embedded in OS/2 version 2.0 and higher.

If you have any further questions, please contact me.




LADDR
October 26 1990
Page Two


LADDR Background
----------------
The LADDR architecture has three main levels of software modules, as shown
below.  It separates the operation of peripherals from the connection issue
of being able to "talk" to a certain HBA.

The important point is that Western Digital is responsible for being able to
connect to LADDR via a BID, but is not responsible for disk, tape, etc.,
drivers to support peripherals.  That is the job of Microsoft and
Independent Software Vendors (ISVs) that support that type of peripheral, or
the peripheral manufacturer.

        .
        .
        .
        |
        OS         +-----------+
        |          |   OS/2    | The file system issues requests
        |          |FILE SYSTEM| to the drivers.
        |          +-----------+
----------------         |
        |      +-+  +---------+  Type Specific Driver-
        |      | |--|   TSD   |  The software connection for a type of
        |      | |  +---------+  peripheral, such as disk, tape, or CD-ROM.
        |      | |       |
        |      |I|  +---------+  Vendor Specific Driver-
      LADDR    |O|--|   VSD   |  Drivers that modify or enhance the operation
       (OS)    |S|  +---------+  of a type of peripheral.  This adds features
        |      | |       |       or corrects incompatibilities.
        |      | |       |
        |      | |  +---------+  Bus Interface Driver-
        |      | |--|   BID   |  Software to connect specific host adapters
        |      +-+  +---------+  to the OS.
---------------          |
        |       +------------------+    +----------+ +----------+ +----------+
        |       |     SCSI HBA     |----|   SCSI   |-|   SCSI   |-|   SCSI   |
    Hardware    |                  |    |PERIPHERAL| |PERIPHERAL| |PERIPHERAL|
        |       +---------+     +--+    +----------+ +----------+ +----------+
        |                 +-----+
        .
        .
        .


LADDR
October 26 1990
Page Three


LADDR Background  (Cont.)
-------------------------
The user adds to his/her config.sys file on the PC the LADDR files. Only the
required files are installed.  Here are some examples.


The files required for disk drive operation under LADDR are:

     BASEDD01.SYS      supplied by Microsoft
        IOS12.SYS      supplied by Microsoft
     IOCONFIG.SYS      supplied by Microsoft
     WD7000AX.BID      supplied by WD
      STDDISK.VSD      supplied by Microsoft
         DISK.TSD      supplied by Microsoft

For CD-ROM operation you need, in addition to disk files:

        CDROM.VSD      supplied by Microsoft
        CDROM.TSD      supplied by Microsoft
        CDROM.FSD      supplied by Microsoft, this is installable file system

For DAT tape drive operation you need, in addition to disk files:

     DATTAPE.VSD       supplied by tape drive vendor
     DATTAPE.TSD       supplied by tape drive vendor (eventually by Microsoft)
     Backup Program    supplied by tape drive vendor, or purchased independently