5 1/4 diskettes available

[Chuck Guzis]

On 7/10/19 7:14 PM, Fred Cisin via cctalk wrote:
>>> They have hub rings, so they are probably 360K

To add a bit to Fred's excellent explanation, I can offer the following:

While the hub ring is *generally* a good indicator of "2D" versus "HD"
disks, I've seen exceptions.  Early 2D floppies did not use the hub ring
and I've got a few HD ones that do.  The hub ring thing is a story in
itself, which I've gone into in the past.

So, basically, what matters is how the cookie is punched and what the
characteristics of the brown schmoo that it's been coated with.
High-density diskettes use a coating that contains smaller particles, is
generally thinner and of higher magnetic coercivity ("stiffer") nature.

The punching has to do with "hard" sectoring vs. "soft" sectoring.  In
the former, as Fred mentioned, there is an extra hole (in addition to
the index hole) in the cookie for each sector.  Most 5.25" media is
soft-sectored.  You can tell the difference by holding the jacket of a
floppy with one hand and rotating the cookie by the hub with the other.
If you only see one hole appearing through the jacket aperture with
every revolution, the disk is soft-sectored.

Beyond that, you can forget the "tracks".   The same floppy can be used
in 80 track (96 track per inch) as well as 77 track (100 tracks per
inch) as well as 40 track (48 tracks per inch) drives.

5.25" diskettes are only a bit more complicated than 3.5" ones, where
you need only worry about the coating characteristics.

Having said that, there *are* oddball exceptions, but you're unlikely to
run into them in real life.

8" diskettes on the other hand, employ only one coating type, but use
the index hole to indicate single-sided, vs. double-sided and density,
as well as hard- vs. soft-sectoring and "flippy" floppies.

Again, there are the "oddball" cases, such as the Vydec floppies that
put the sector holes on the outer edge of the cookie or Memorex 650
disks that have a "dogleg" in the jacket outline, but you likely won't
run into those.

--Chuck