floppy controller IC (was Re: Fixing a PET?)

From: Richard Erlacher <edick_at_idcomm.com>
Date: Thu Sep 30 10:07:16 1999

Without beating this dead horse too much more, I'd like to add a couple of
things to the mix.

(1) I've successfully formatted DSDD diskettes to 1.2MB DSHD format. I have
also formatted DSHD diskettes to DSDD 40-track and 80-track formats, with
varying degrees of success, depending on how carefully I tracked WHERE they
had been formatted.

(2) This gives rise to at least two other points which probably need to be
stirred into the mix. (a) The drive in which the diskette was formatted
determines what kind of drive will read/write it successfully. Formatting
as DSHD must take place in a 1.2MB drive. If the lower density is to be
used successfully, care must be taken to ensure that the disketted is never
written in a DSDD drive, as the heads are different and the DSHD drive can't
erase enough of what the DSDD drive's heads have written to be completely
successful all the time. (b) WHEN the diskette was made seems to make a
great deal of difference as to whether this (item #1, above) will work, i.e.
whether the DSDD diskettes will format to DSHD with whatever massaging is
required.

Eric's comments about the emulsion placed on the media is quite correct. At
some point, however, it became economically expedient to use the same
emulsion in all of their (the diskette-makers') products as opposed to
producing two different emulsions. That led to another period during which
the bin-sorting provided a market for lots which were only slightly less
"perfect" than their standards demanded, and these were then used, together
with whatever completely adequate lots were necessary to meet the demand for
DSDD media. The "perfect" lots of stock were punched and labeled DSHD.

Clearly, a goodly portion of the time, DSDD media were sold which were
completely adequate to meet DSHD requirements.

Since the DYSAN folks in Luisville, CO, who were once a customer of mine,
practiced this in fixed disk media, I doubt it was done any differently with
floppy media . . . perhaps not, but it makes sense.

Dick

-----Original Message-----
From: Eric Smith <eric_at_brouhaha.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Thursday, September 30, 1999 4:08 AM
Subject: Re: floppy controller IC (was Re: Fixing a PET?)


>Glen wrote:
>> BTW my understanding is that all 5.25 diskettes made today are
bin-sorted --
>> that is, they shoot for DSHD and the fallouts are sold as DSDD.
>
>I don't believe that for an instant.
>
>High-density requires a different, higher-coercivity coating, which will
>not work properly for low density (single or double).
>
>However, there's no difference between double density 40 track and 80 track
>disks. They aren't even binned; they just get labelled differently.
>
Received on Thu Sep 30 1999 - 10:07:16 BST