Date   : Sat, 16 Oct 1982 02:36:00-EDT
From   : Frank J Wancho <FJW@Mit-Mc>
Subject: 80 TRK Mod and "N" drives

    I have followed the directions given below for the 80 track mod and
    all seems to work!

--Frank

El Paso, Tx, 14-Oct-82

The following is a description on how to use full 80 track
capabilities of disk drives like the TANDON TM 100-2 on a North Star
CP/M system using North Star CP/M 2.2 Release 1.1.0.  The
modifications worked when I checked it out initially, but only
constant use of the 80-track system will reveal any bugs.  Therefore,
I can assume no liabilities whatsoever, nor guarantee that the mod
will work for your particular system in any way.

If you are NOT using dual sided drives capable of stepping 40 tracks
per side, or if you are NOT using North Star's CP/M rel. 1.1.0 QD,
then it is time for you to hit Control-C, otherwise read on.

The following steps will guide you through the modification:

1.  Prepare a SYSGEN image of the system you are currently using and
    name it SYS70.COM.

2.  Load SYS70.COM using  A>DDT SYS70.COM.

3.  With the "S" command in DDT make the following changes:

-S2C05
2C05 22 27 <= change max front side track from 34 to 39 (decimal)
2C06 ?? .
-S2C0B
2C0B 23 28 <= change max number of tracks/side from 35 to 40 (decimal)
2C0C ?? .
-S3013
3013 A9 C2 <= change disk length (max CP/M sector)
3013 ?? .
-^C
A>SAVE 70 SYS80.COM

4.  Execute the file SYS80.COM and put the modified system on drive
    A:, then cold-boot.  Your CP/M is now set up to utilize all 80
    tracks on a 48 TPI DSDD drive.  Please note than NO conversion is
    needed to use all 160 Tracks on a 96 TPI drive (such as TM 100-4).

5.  >>>>> IMPORTANT <<<<<
    You are now accessing uninitialized areas of a diskette.  You will
    have to convert all your diskettes from 70- to 80 tracks!  To do
    this, you will have to transfer the contents of one DSDD disk to
    two SSDD disks using the 70 TRACK SYSTEM, and then copy the files
    back to a freshly formatted disk using the 80 TRACK SYSTEM.  While
    this may be somewhat confusing and quite time-consuming, I think
    it is worth doing, since you get an extra 50k per diskette for
    your efforts.  The tradeoff is incompatibility of DSDD diskettes
    with others.  To remedy that, either exchange only SS disks, or
    reformat them when necessary.

To further test this modification, I will soon convert all disks on
the B: drive of the El Paso RCPM to 80 tracks.

                                               Happy hacking!


Oh, and many thanks to whoever enabled me to do this by providing me
with some insight into the workings of the BIOS.....


El Paso, Tx, 14-Oct-82

This file contains information on how to convert North Star's
FORMAT.COM to format 80 track drives.  As with NS80TRK.MOD, these
modification are tested but can NOT BE GUARANTEED TO WORK FOR YOU!

1.  Modification of FORMAT.COM (for N* CP/M 2.2 rel 1.1.0. ONLY!!!)
for use with a modified CP/M BIOS which allows 80 track drives:

This is the sequence of commands to do it:

A>DDT FORMAT.COM
 ....
-S1EB
01EB 45 4F  <= change max track from 69 to 79
01EC ?? .
-S72E
072E 37 38  <= change display so it says "... 80 tracks..."
072F ?? .
-^C
A>SAVE 9 FORMAT80.COM

This completes the conversion.  Note that FORMAT will still correctly
format single-sided diskettes.


2.  North Star has an undocumented feature in rel. 1.1.0.  This
    feature is the so-called "Nine"-drives.  That means that N* CP/M
    2.2, rel 1.1.0.  is able to control 96 TPI drives.  I have not
    been able to check this out, but see no reason why it shouldn't
    work.  You HAVE TO designate a 96 TPI drive as such and will not
    be able to use any other than a 96 TPI diskette on it.  To do
    this, answer the DRIVE-question in CPMGEN with a "N" instead of
    "D" or "Q".  (You can't fool the system - have to have a real 96
    TPI dual sided drive!)

    In order to format a diskette in "N"-format, you have to modify
    FORMAT.COM.  FORMAT.COM is already prepared to handle N-drives.
    It will even offer this function if you respond with "9" when
    asked for the disk format.  However, it's internal workings
    require your response to be "N", which is normally rejected.  To
    make it accept "N" instead of "9" and be able to format N-drives,
    use DDT to change byte 01F9H from 39H to 4EH.  Then you'll be able
    to use FORMAT.COM with 96 TPI drives.

                                               Again,
                                                       Happy hacking!