For the TI, sector sizes are always 256 bytes. That means that for a 3.5" HD drive, we have 5760 sectors - if we had a suitable controller. The HFDC, for instance, could be able to handle it, but its data separator must be replaced.
The Myarc HFDC has a HDC9234 controller chip (from SMC). The Corcomp controller has a WD2793 or a WD17** chip (don't remember); the Myarc DDCC-1 has a WD1770. Note that the 1771 is the only one called "FD".
From that wiki page, I was going by this: For example, the HD format of 3 1⁄2-inch floppy disks uses 512 bytes per sector, 18 sectors per track, 80 tracks per side and two sides, for a total of 1,474,560 bytes per disk. But if the TI is always limited to 256 bytes per track (TI computer, or TI controller, were you saying?), then to get to the 720/1.44 for the 3 1/2" you'd have to be 36 sectors per track, 80 tracks. (If double density is 18 vs 9 sectors per track, then what some called QD would make sense for 36 sectors per track. Wonder why that article implied that it was 512 bytes per sector, but still with 80 tracks and 18 sectors per track.) Either way gets you to 720 SS and 1.44 DS, I suppose.
Edited by patrickmcmichael, Wed Apr 3, 2019 4:25 PM.