On Mon, Feb 27, 2023 at 9:30 AM Chuck Guzis <ccl...@sydex.com> wrote:

> On 2/27/23 06:50, Warner Losh wrote:
>
> > You should be using QD floppies, but those are rare. DD floppies from
> > later than
> > 1985 though work just fine (discovered empirically while  a poor college
> > student,
> > reconfirmed recently when I made all those Venix disks).
>
> Speaking from experience and consultations during the 1970s with
> engineers from Dysan (we were using 100 tpi drives), the only difference
> between QD and DD floppies is QA step--QD ones are usually verified at
> 96 or 100 tpi, the DD ones at 48 tpi.  The brown goo spread on the
> doughnut is exactly the same.
>

Prior to about 1984 or 85, the failure rate for DD floppies for me was
high enough that I splurged for the QD. After 84 or 85, I never had any
problems
using DD media. I suspect that yields must have gotten better, but maybe I
just had bad luck prior to going to college...


> If one purchased factory-formatted diskettes for a specific platform, of
> course the formatting would be different depending on the platform.
>

True. For the Rainbow I was always reformatting because nobody sold
pre-formatted Rainbow disks at a price that was sane.


> Similarly SS and DS diskettes are identical; early on, ones with
> verification errors on one side were "flipped" accordingly and sold as
> SS. As techniques improved, the only difference became the label.
>

I believe that..

Warner

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