TEAC FD-55F floppy drives https://retrocmp.de/fdd/teac/fd55f.htm
The TEAC FD-55F never appeared in the world of IBM compatible computers. Why is that? Because it was simply superfluous in the DOS world. The TEAC FD-55F is a double-sided 5.25 inch drive that can write 96 tracks per inch (TPI) with 9 sectors per track. In other words, the capacity of a floppy disk is 720 KByte. There were Radio Shack and other computers (NCR, etc.) that used this format (DSQD). This corresponds to the capacity of the standard 3.5-inch double-density (DD) drive. The 3.5-inch floppy disk format was supported since DOS version 3.2. Introduction of 3.5” drives and disks by IBM (mid-1980s) was one reason why the 5.25 inch drives with 720 KByte storage did not find their way into the IBM world. == Further in the above web link: Changing a Teac FD-55GFR drive to a FD-55F drive ... or, How do I get my drive to spin at 300 RPM instead of 360 RPM ? gb
