Dec 102017
Text files about how to install more than two MFM Hard disks in PC.
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Text files about how to install more than two MFM Hard disks in PC.
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How to run 3 or more MFM hard disks on an AT type machine
By Bruce Travers
CompuServe: 72215,1272


I recently upgraded from a Tandy 3000 to a 80386 20mhz clone.
Everyone knows that if you have a 80386, you must have at least 150mb
(grin) or people will turn up their noses at your system. My two 45mb
Rodime drives only added up to 90mb so I was compelled to increase my
storage capacity. The options were to sell one or more of the Rodimes
and buy bigger (read expen$ive) drives, or to just buy another low
cost hard drive and attempt to make it work.

The task was supposed to be easy. Before I had the 3000, I was
running a model 4 with 4 hard drives attached. The model 4 controller
supported 4 drives so it is to be assumed that the AT would do the
same. Well, you know what they say about the 'ass-u-me' word. Actually,
I knew before hand that the task might pose an interesting problem so
I opted to buy a third hard drive anyway.

My purchase was an 80mb (to give 170mb total) Seagate ST-4096. It
is kinda slow for my machine but I really only use it for archival
purposes. It beats a tape drive anyway.

I'll not get into how many different configurations I tried to
get it to work and instead jump to the solution:

The Solution:

You need the following:

2 hard disk controllers. At least one of them must be able to
be jumpered to use a different I/O and ROM address area. I chose the
WD1003-MM2 (since it came with my machine) and the WD1004A-WX1. The
WD1004 was chosen after a brief discussion with Western Digital about
relocating the I/O and ROM.

3 or more hard disk drives. If you only have 2 drives then why
are you reading this document ?

Disk Manager by Ontrack Computer Systems, Inc. This should have
come with your drive if you purchased a well know brand. If not then
you can get their Generic Disk Manager for $129.95 U.S. funds. The
latest number I have for Ontrack is 612-937-1107.

The following step by step instructions assume (ooohhh that word
again) that you are setting up the disk system(s) from scratch. If you
already have a 2 drive AT system running, then jump to step 4:

1 - Install the AT hard disk controller in your machine. Consult
your controller manual (contact your dealer if you did not get the
manual) for proper configuration and jumper settings. In my case this
required the 2 Rodime drives to be configured as drive 2 and the
cables be plugged into the WD1003.

2 - Use your AT setup program and identify the 2 drives to your
machine. If your dealer has not already done so, you need to low level
format your drives, then partition them, then high level format them.
If you are using DOS 4.0, I would suggest makeing each logical drive
equal in size to the physical drive. This way your first drive will be
C and your second drive will be D.

3 - Verify that your first 2 physical drives can be accessed from
DOS. Only when you are sure that your 2 drive system is working should
you proceed to step 4.

4 - Properly jumper your second controller to use I/O 0324h and
(if required) ROM location CA00h. On the WD-1004A-WX1 you place a
jumper on W21.

5 - Install the second controller as per your controller
manual. Note that you should install it as if it was the only one
in the system. Ignore your primary controller and the cables that
go with it. In my case, I did not use a twisted 34 pin cable so
I jumpered the ST-4096 as drive "1" (not "3" as one would assume).

6 - Run your setup program and tell your AT that it has only
1 hard disk. This will temporarily turn off your second drive (on the
first controller) so that DOS may access the third drive. You will
need to leave the first drive (on the first controller) identified to
the AT so you can boot off it instead of floppy.

7 - Boot your machine. You should have a C drive but no D
or E (again assuming 1 logical disk = 1 physical disk).

8 - Go into DEBUG and jump to the controller format routine
(in the case of the 1004 as configured, type G=CA00:5 and press enter).

9 - Low level format the drive by using the built in controller
firmware. Follow the instructions in the 1004 manual and do not
do a virtual split of the drive.

10 - Use DOSs FDISK facility to create partitions on your
third drive, which DOS now sees as drive 2. Note: Do not make any
partition greater than 32mb as Disk Manager will not work with it.
Disk Manager 4.0 may work, but as I only have 3.2 for the Seagate
drive, I can not comment.

11 - Use DOSs FORMAT command to format all your logical drives
on your third (first on controller #2) disk. Once this is done, you
should see your first disk on the first controller as drive C, then
your third disk (first on the second controller) as drive D, E, F and
so on.

12 - Modify your CONFIG.SYS file on your C disk root directory.
the first line should read: DEVICE = DMDRVR.BIN which will invoke
Disk Manager when you boot. Copy the DMDRVR.BIN file from your Disk
Manager master diskette onto your root directory of drive C.

13 - Run your setup program and tell it that you have 2 drives
attached to your AT. This will bring back the second drive from the
first controller now that the third drive (first on second controller)
is properly set up.

14 - Boot your machine and you should now be able to access your
first drive as C, second drive as D, and third drive as E, F, G, etc..
depending on how many <32mb partitions are set up.

Theory of Operation:

I really do not know why this works. Everyone has been telling
me that it is impossible. All I can say is that the people at Ontrack
have built this feature into Disk Manager but don't advertise the
fact too much. Note that I never used Disk Manager to set up any part
of the disks, but I used their driver DMDRVR.BIN to make DOS see the
third drive (first on the second controller).


There are a few problems which I can live with:

1: My data transfer rate on the third drive is about 1/3 to 1/2
that of the 2 drives on the AT controller. Probably due to 8 bit vs
16 bit transfers.

2: A mysterious drive E: has appeared which locks the machine
if I try to access it. Looking at the partition table in Disk Manager
shows a small partition near the start of the disk. This is used by
the 1004 controller to tell what type of drive is installed (since this
controller can install drives dynamically). It could be that Disk
Manager is being fooled and tries to make it available to DOS
as drive E:

3: I hate having 3 partitions on my third drive using DOS 4.0
(but again, this is the only way it could work with Disk Manager 3.2).
Hopefully when the Seagate version 4.0 of Disk Manager comes out, I
can repeat the above procedure using the full disk for a partition.

4: The system hangs for about 30 seconds at POST time
when the WD-1004A-WX1 searches for a second (fourth) disk drive. This
probably will not happen if you have 2 drives attached to the 1004.
Note that no error is returned, it just takes its sweet time.

5: If you try to do the above instructions out of sequence,
then chances are your system will lock up and you will have to remove
the second controller to access your disks again. I found this out
many many many times.


The 1004 controller can be jumpered to run from the following

C800/320, CA00/0324, CC00/0328, and CE00/032C

so theoretically it should be possible to run 3 1004 controllers
with 1 AT controller and get a total of 8 mfm hard drives running on
your machine! But then again, that would take one huge tower case to
hold it all in.

I hope this little document is not too obscure. Many things
are assumed (argggghhhh) and you should have knowledge about how to
muck around inside your PC before attempting any of this. If you
try to get something like this going, feel free to drop me a note
at either CompuServe or GEnie at the addresses listed on top. I'll
try to help out if I can.

- Bruce (08/13/89)

 December 10, 2017  Add comments

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