Re: High and Double density floppies

[dchiu@netcom.com (David C.W. Chiu)]

In article <dgaxiola.12.006C140A@mit.edu> dgaxiola@mit.edu (David Gaxiola) writes:
>In article <jolomoCLL3w2.67G@netcom.com> jolomo@netcom.com (Joe Morris) writes:
>>Question: why can't disk][ drives format high density floppies at 140K?

Because High Density floppies uses different coating formula in the media. 
Someone else who is more technically inclined can probably offer a much more
meaningful explaination.

>Don't disk ][ drives need hard sectored floppies?  There's a small hole to the 
>right of the main hole in the center of the disk.  As you rotate the disk 
>by hand you'll notice that there's a small puncture in the disk that 
>you can see through every now and then.  Soft sectored floppies (I think) have 
>this hole only once.  Hard sectored disks have this hole several times.  Older 
>disks needed to see these holes many times to get in sync.  Newer, high 
>density disks, only have a single hole and won't work with the old disk ][ 
>drive.  Is this correct or is my memory bad?

Disk II/Apple II uses software scheme to identify start of a track on 
floppy, so it does not use sector holes at all. That is to say, Disk II 
doesn't care if you are using hard sector or soft sector media. People 
who are interested in all the glorious details about this software scheme 
should consult Beneath Apple DOS or Beneath  ProDOS. (Great books BTW)