               Installing a 1.44Mb 3.5 inch floppy drive
                          by Steven Greenberg

There's been a bit of discussion about 3.5 inch drives lately, so I 
thought I'd pass along what works for me.

My goal was to get a 1.44Mb 3.5 inch drive working with my IBM AT 
compatible computer.  While there have been a number of 3.5 inch floppy 
drives on the market for a couple of years, they have been only the 
720Kb size.  I wanted to get the 1.44Mb capacity drive for the following 
reasons: 

1) Backup.  Right now most people are backing up their PC's hard drives 
onto floppy diskettes.  Owners of AT's use their 1.2Mb 5.25 inch drive 
for this purpose.  I was hesitant to get this drive because it can't 
write to a 360Kb 5.25 inch floppy drive in a reliable fashion.  The 
problem is that a 1.2Mb drive has 80 tracks per inch (tpi) and it's 
read/write head is sized to fit this width track.  A 360Kb drive has 40 
tpi and the tracks it's read/write heads create are twice as wide as the 
track made by the 80 tpi drive.  When a 1.2Mb drive writes a diskette in 
the 360Kb format, it places the tracks in the right position - but it
does so with narrow tracks.  If you were to then try to read this 
diskette in a 360Kb drive, it might or might not work.  If your 360kb 
drive is correctly aligned, then it will stay right in the middle of the 
narrow track and pick up the information just fine.  But, if the drive 
is not properly aligned, then the read/write heads may stray to one side 
and miss the narrow track (it probably isn't far enough off to miss the 
wide 40 tpi tracks).  Old full-height 360Kb drives are notorious for 
getting out of alignment very easily.  I don't want to take the chance 
that a diskette I send someone may not work.  I therefore installed a 
360Kb 5.25 inch diskette drive, which I use to load software onto my 
hard drive and to create diskettes that are to be sent to others.

Now, with the 1.2Mb drive being cut off my list, I don't have a large 
capacity drive to use to back-up my hard drive.  (The 360Kb drive 
requires way too many diskettes to do the job.)  The capacity of the 
1.44Mb 3.5 inch drive suddenly becomes VERY appealing.  I only need one 
1.44Mb diskette for every four 360Kb diskettes needed before.  Also, the 
3.5 inch media is much hardier the the 5.25 inch media, because it's 
encased in a hard plastic shell and has a metal shutter that covers the 
opening for the read/write heads.  1.44Mb is the way to go for floppy 
back-up's!

2) Laptop compatibility.  Almost all of the laptop computers that are so 
popular now use 720Kb 3.5 inch drives.  I wanted to be able to exchange 
diskettes with this type of machine.  The 1.44Mb 3.5 inch drive is able 
to RELIABLY read and write both 1.44Mb and 720Kb 3.5 inch disks.  The 
problem that occurs with the 1.2Mb 5.25 inch drives trying to create 
360Kb diskettes does not happen when the 1.44Mb drive creates 720Kb 
diskettes.  There is no problem because a 720Kb diskette, when used with 
PC/MS-DOS, has 80 tracks and 9 sectors per track.  A 1.44Mb diskette 
also has 80 tracks, but instead has double the number of sectors - 18 
per track.  Thus the width of the track remains constant between the two 
formats, while the capacity doubles due to twice the number of sectors.  
So with the one drive I'm able to use both of the prevailing 3.5 inch 
PC/MS-DOS standards.

3) PS/2 compatibility.  The IBM PS/2 computers use 1.44Mb 3.5 inch 
diskettes.  I'm able to interchange floppies back and forth with no 
problems at all. 

To accomplish my goal, I looked at the Teac and Toshiba 1.44Mb 3.5 inch 
drives.  The drive I ended up using is the Toshiba, Model #4603A0K, 
which is a 1/3 height 3.5 inch floppy drive.  This drive is one of their 
more recent models and has a media sensor to determine capacity (see 
below).  I didn't use the Teac because of the terrible supply problems 
Teac is having with their drive.  I mounted the drive in a Toshiba 5.25 
inch mounting kit (Part #352KU).  This kit allows the smaller drive to 
be installed in the same place that a standard 5.25 inch drive fits.  
The kit has faceplates in black or gray and includes the necessary rails 
for the AT.  The kit also adapts the connectors, signal and power, to 
the same size/shape that 5.25 inch drives use.  I paid $135 for the 
drive and kit together - but I hear that they are available for as low 
as $110.

After installing the drive in the kit, as per the instructions provided, 
I set the jumper on the kit's signal adapter card to B (NOT A as 
instructed!).  This jumper controls whether the drive informs the 
computer when a diskette has be removed from the drive.  In the B 
position the drive DOES tell when a diskette has been changed, so that 
DOS knows to re-read the directory.

Next, on the bottom of the drive were        Factory         Correct
two jumpers.  They came from the            ----------      ----------
factory set to C and DS1.  Set them         O  O  O  O      O  O--O  O
to B and DS2.  This sets it to                 |     |                      
Drive Select 2 and tells it to look         O  O  O  O      O  O  O--O
at the media to determine which capacity 
to use - 720Kb or 1.44Mb.  The first 1.44Mb drives that came to market 
relied on Pin 2 of the hard drive controller to inform the drive of the 
proper capacity.  Unfortunately most AT hard drive controllers don't 
provide this signal.  This model has a sensor that can look at the 3.5 
inch diskette and tell which is which.  (The 1.44Mb diskette has a hole 
on the opposite side of the write protect hole, that is not present on 
the 720Kb diskette.)

After doing this, the drive was installed into the computer.  In this 
case the computer was an Everex System 1800A.  With this computer the 
drive could be used either as a 720Kb only, or as a 720Kb/1.44Mb drive.  
The difference depends on a couple of factors.  First, DOS 3.2 only 
supports the 720Kb format.  DOS 3.3 supports the 720Kb and/or the 1.44Mb 
format.  (If you are using an older version of DOS, such as DOS 3.1, 
then you will need to upgrade in order to use 3.5 inch diskettes.)   I 
chose to use the PC/MS-DOS 3.31 marketed by Compaq Computer because of 
their reputation for good quality, good manuals, and because IBM's 3.3 
has lot's of bugs!
.
Second, the ROM BIOS of this computer had to be upgraded.  The AMI-B 
BIOS did not support 3.5 inch drives at all.  The AMI-C supported 720Kb 
only.  The AMI-D BIOS supports 720Kb and/or 1.44Mb.  The AMI-D was 
chosen for this installation.  I was charged $40 to upgrade the BIOS, 
but anyone purchasing a new Everex System 1800 should get the AMI-D as 
standard.  The BIOS identifies itself during the booting process.  With 
BIOS supporting the drive directly, I was able to boot up and use the 
1.44Mb 3.5 inch drive (as Drive B:) immediately.  With computers that 
don't have BIOS support you will need to use the DOS Driver.Sys command 
in order to get the drive to work.

Now everything is working just fine, and I can exchange diskettes with 
just about any PC compatible computer in the country!  I should also 
mention that the 1.44Mb 3.5 inch drives work only with AT and 386 type 
machines because they transfer information at 500Kbs (1000 bits per 
second) to and from their floppy drives.  PC type computers only 
transfer information at 250Kbs, through I hear that some new floppy 
drive controllers are coming on the market that do support 500Kbs.  

I hope that this information helps you decide how to configure the 
drives in your computer.  If you have questions, I can be reached via 
the MSPCUG Bulletin Board (415) 927-1216.  Leave a message for Steven 
Greenberg.
