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.