I've got the reference manual for the 2.8MB one. How was the embedded servo recorded--and in what format?
That must indicate the formatted capacity. The two Drivetec models came in unformatted capacities of 3.3 and 6.6 MB. Marketing hype...
The embedded servo info was written by some pretty heavy duty and precise mechanical gear, which of course, added to the high cost of the media. And the process was fairly slow. Taking several minutes per disk. As noted in another post, the servo bursts were written "straddling" the tracks so when centered over a data track, you would read equal amplitude from each burst. The actual data format was MFM, same as the standard floppies of the day.
One thing I noted in one of the posts, poster said the drive spun at 600 rpm. That was only true when reading 1.2MB or 400/800K disks. The Drivetec disk was read at 360 rpm. The higher bit density and rotational speed meant that data came off the disk at the same data rate as the older 8 inch floppies and twice the rate of the standard 5-1/4 in floppies. We sped up the spindle speed to keep the higher data rate and improve the amplitude we'd get off the older floppies. Remember, our heads were only half as wide so we'd get less signal at the same speed.
The servo burst themselves consisted of a code to tell us which burst we were reading followed by an area of constant frequency that we used to measure the amplitude.
We tried to prevent accidental formatting. We moved the write protect notch to a) prevent writing older floppies; b) make our disks look write protected in other standard drives. We also added logic in the drive to prevent writing that started at the "Index". In a typical format command, the controller waits the the index signal from the drive, then starts writing the whole track. If we see write gate going active at index, we block it.
Given the nature of the servo, you would need a mechanism that is 384 tpi for the 3.3 and 768 tpi for the 6.6 in order to format a disk. I don't see any practical way to do it in a drive. Then there is the electronics, we wrote both sides nearly at the same time to cut down on the format time. That meant we had two sets of format and verification electronics. We used an optical shaft encoder to give us angular position to insure we got the servo burst and data portions in the right place.
Hopefully that helps. I apologize if I misinterpreted your question. Feel free to ping me if you want more. May take me a bit shake out some of the cobwebs.