IBM 9331-011 8" External Floppy Drive - eBay 183038271095

Fred Cisin cisin at
Thu Feb 1 23:39:16 CST 2018

On Thu, 1 Feb 2018, Chuck Guzis via cctalk wrote:
> Yeah, I've got an old ABCD manual printer switch with the "centronics"
> connectors that swaps all 36 lines, but it always seemed like more
> trouble than it was worth, so it resides in a storage cabinet.
> I use a rack-mounted PC with a couple of DC37s on the front panel, so
> swapping boxes is pretty simple.

But, if you don't have one, YOU might like:
I can no longer justify such a purchase  :-(
(More stuff that I used to want)

> I've seen some bizarre stuff, but the one that takes the cake was a boot
> floppy from a PLC.  Said PLC was equipped with two floppy drives--one
> for booting only and the other for user data.   The boot floppy had a
> very oddball track spacing; something like 120 tpi; the user floppy was
> a normal 135 tpi.  This was measured with developer (Kyread) and a
> microscope.  I just couldn't believe that a manufacturer would go to
> that length.
> I guess the PLC manufacturer didn't want their software to be copied.
> Needless to say, replacement boot floppy drives were near unobtanium and
> stupid expensive when you could find one.

That IS weird!
Unless, . . .
In the unlikely event that they were clueless enough to have altered the 
track spacing, but left the rest of the drive and interface alone, in 
which case it could be connected to a "standard" FDC to make an image, and 
maybe even then replace the modified drive with a standard one.
(Or something as terminally weird, like the Tandy PDD1)

When I first got a Micropolis drive, I found "100tpi" hard to believe.
But, interchange attempts showed that by the inner tracks, it was 
not 96tpi, and nor a multiple of 48tpi.
My homemade developer, and my patience to keep trying weren't good enough 
to be able to successfully do other than take their word for how many.
(Seeing the difference between 96tpi and 100tpi should be easier than 
telling the difference between Leica thread (39mm x 26 Whitworth threads 
per inch) V the early Russian Fed (39mm x 1.0m DIN thread)
some of the earliest Canon imitations (39mm x 24tpi thread))

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