On 6/6/2013 3:22 PM, Michael Black wrote:
It's the controller that sets the density. If you look at early floppy disk ICs that do double density, there is a means of switching it between single and double.
This is FM vs. MFM that I talked about in my response. Single/double density all about how "densely" bits are encoded by the controller, and we're generally talking about standard Shugart controllers (nothing to do with Apple). Double density vs. High density indicates track width capability (48TPI vs. 96TPI).
ability to switch density generally went away. I remember lookig at single IC controllers in a databook and noticing that, and there was at least one operating system, FLEX for the 6809, that needed the first sector to be single density for some reason, and the later controllers were incompatible.
The Epson QX-10 shares this capability/requirement. There are others as well.