Date   : Tue, 23 Mar 2010 22:42:54 -0000
From   : profpep@... (Mike Pepper)
Subject: Re-using floppies

> Those Teak drives have standard Shugart interfaces (and were in a nice
> external box) - but if Commodore drives always had special interfaces,
> I'd love to know what else used 100tpi ?
>

The Sord business desktops used them - I had to upgrade a couple of these
machines years ago for a customer. We replaced the full height 77 100TPI
track drives with pairs of 1/2 height 80 track 96 TPI drives, leaving one
old 77 track drive in 1 machine as a copier. The discs ran fine, and the
machines had double the amount of storage. I still have a virtually unused
Teac 77 track drive if anyone needs discs copying. they weren't direct
drive, so the belts need to be checked carefully before being put into
service. Early drives had strobe patterns on the drive pulley. I once
learned the hard way that they were set for 60Hz American mains...... and
had to build my own LED based mini strobe for speed checking. The early
motors were spin off from the cassette business, and some had a hole in one
end for access to the speed trimpot, others had a motor control board.  Some
had brush type motors too, so will eventually wear out. You can build a
reasonable substitue servo controller. I still have a couple of alignment
discs too. These can't be copied, because there are tracks with raw analogue
data on them for head alignment. You either had to make a switch box to
control the drive and to step the heads in and out, or had to buy a
frighteningly expensive disc exerciser. I built one from an Elektor design.
Nowadays some code on a PC would suffice, I guess.

||\/||ike

The Apple ][ and the ACT Sirius both used variable speed drives, making
copying something of a nightmare. I need to resurrect an Apple ][ soon to
copy up some old Apple Syntauri music discs, (Joy!)

The really wierd area of floppy disc history is in the early days of the
smaller discs, with HP/Sony doing a 100K single sided one, and then slowly
pushing the capacity. Since early HP disc packs used the 488 bus, with on
board intelligence, so upgrading drives means firmware patching - not nice.
When the experimental 3 inch discs turned up and didn't catch on, Alan Sugar
bought up a load cheap to use in his Amstrad word processor. There were a
whole load of formats for these too - I have about 4 various units,
including a pair in a case for BBC use.