Getting familiar with the TI-99/4A and Floppy Drives

(updated Jan 7, 2018)


Floppy drives can be pretty confusing.  I hope to help clear up some of that.  Possible make it worse, but that’s for you to decide.

Let’s start with some definitions:

Common Floppy Drive Characteristics and abbreviations:

SD = Single Density

DD = Double Density

HD = High Density

SS = Single Sided

DS = Double Sided

Now, you’ll often see description of drives, such as:

SSSD = Single Sided Single Density

DSSD = Double Sided Single Density

DSDD = Double Sided Double Density

DSHD = Double Sided High Density

There are probably others out there, but those are the most common ones you’ll run across.

(Under Construction - BUT more to come!)



The TI and the original TI Floppy Disk Controller (TI-FDC) are ONLY capable of SSSD and DSSD modes.

That means that you can only utilize 90k and 180k drive capacities.

That DOES NOT mean you can’t use 360k drives, YOU CAN, but the maximum capacity will only be 90k for single-sided, and 180k for double-sided.  It will NOT take advantage of the double-density modes that a DSDD drive (360k) can offer.  That’s good, because you can use almost any IBM PC 360k drive on the TI.

There is an 80-track upgrade, but that’s for another discussion, as it requires desoldering the old ROM chips and installing upgraded ones.  I’m not sure it’s worth the effort.  In my opinion there are better ways, to get more bang for your buck.

TI Floppy Disk Controller:

1.44MB 3.5” ‘High Density’ drives, will work on the TI, they just won’t work in “high density” mode.  You’ll still be limited to 90k, and 180k formatting capacity.  A great alternative to 5.25” drives.  They’re smaller, quieter, less error prone, and more durable.

720KB 3.5” Drives; these are your best choice for 3.5” drives.  However, they pretty much don’t exist anywhere.  Good luck finding one or more!  Fully compatible with the TI in 90k, and 180k modes.

3.5” Floppy Drives:

Termination, this is where things get interesting.  I’ll try my best to explain, but it gets confusing real quick.

All TI-FDC connected drives need to have termination at the end of the “chain”.  The chain, is considered the physical cable, and termination is usually done by means of a resistor pack on the last drive of the chain, and NOT on any of the others.

There’s SO much more to all this, please be patient until I can add more, hit up Google in the meantime.

(Under Construction - BUT more to come!)

Floppy Drive Termination:

New additions (downloadable PDF’s)

MICROpendium - Chaining Disk Drives - Part I (July 1990, pg. 26)Floppy_Drives_files/200907.MicroPENDIUM%20-%20Chaining%20Disk%20Drives%20-%20Part%20A.pdf
MICROpendium - Chaining Disk Drives - Part II (August 1990, pg. 32)Floppy_Drives_files/200907.MicroPENDIUM%20-%20Chaining%20Disk%20Drives%20-%20Part%20A_1.pdf
MICROpendium - Disk Drivin’ (July 1988, pg.27)Floppy_Drives_files/198812.MicroPENDIUM%20-%20Disk%20Drivin%27.pdf
Disk Drive Compatibility - Glen Fredisks (1987 Sheboygan Area 99er UG Newsletter)Floppy_Drives_files/List%20of%20PE%20Box%20Compatible%20Disk%20Drives.pdf
Floppy Drive - How to Connect Guide.pdfFloppy_Drives_files/Floppy%20Drive%20-%20How%20to%20Connect%20Guide.pdf
Floppy User Guide - by Michael Haardt, Alain Knaff, and David C. Niemi (March 27, 2007)Floppy_Drives_files/The%20Floppy%20User%20Guide.pdf
Mitsubishi MF504B Settings.pdfFloppy_Drives_files/Mitsubishi%20MF504B%20Settings.pdf
Using a 3.5” Floppy Drive on the TI-99/4A - by Marc Hull, Jon Vogel, and Tony Knerr)Floppy_Drives_files/ti_35_inch_floppy.pdf