Hard-sector discs -- how many sectors?

Hi guys, I'm just putting the finishing touches on my disc reader hardware. At this point the disc stepping works (under the control of the FPGA -- you set the step rate and tell it how many steps to move and in which direction), and I can access the acquisition RAM on the PC (both read and write). So the next step before adding the acquisition module is to make the thing detect start and stop events. Frankly if you're reading formats that are index-synchronised (read: IBM PC), then it makes more sense to read index-to-index than it does to read from $HEAD_POSITION to some other random place on the disc. Most folks who have been following this project will know that it has three ways of starting or stopping an acquisition: - Index Synchronised. Waits for one or more index pulses. - MFM Synchronised. Waits for a given MFM sync word to pass under the head. - HSTMD. Hard Sector Track Mark Detector. Looks for an index pulse halfway between two other index pulses, then triggers on the index pulse after that. For example... I I I I I I ... | | X +--trigger here (X = the track index mark, + = the trigger point) Each of these trigger modes can be used in conjunction with a "delayed capture" mode -- basically, it waits for N events before triggering. That is to say, you can program it to trigger on index pulses, with a count of (say) 3, and it'll wait for 3 index pulses before triggering. This could be useful for any number of things -- reading hard-sectored discs, waiting for a few rotations before trying to read the disc, and probably a few other things I haven't thought of yet. I'll probably have the HSTMD detector wait for a track-mark, then count index pulses, which would allow single sectors on hard-sectored discs to be read with very little effort. This seems more useful to me than just counting track-marks. The thing is, I have a limited number of bits available in the registers (and an equally, if not more limited number of registers). So what I want to know is... how high does the event counter need to go? Specifically, how many sectors can you actually get on a hard-sectored disc? I know 10- and 16-sector discs were (are?) available, but were any larger sizes (e.g. 20 or 30 sectors) ever made? Thanks, -- Phil. classiccmp at philpem.me.uk http://www.philpem.me.uk/