Date   : Wed, 24 Mar 2010 19:32:48 +0000
From   : beeb@... (Dr. David Alan Gilbert)
Subject: Re-using floppies

* Mike Pepper (profpep@...) wrote:
> > 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.

Thanks! That's the first information I'd seen about a use of them.

> 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.

We had the service manual for the Teac drives and that's how we figured out
these drives were 100TPI - the symptom of them only reading discs upto a few
tracks in would have baffled us otherwise.
(We did once have to replace the IR LED on the sector hole which went!)

> 
> ||\/||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!)

I have an Apple ][c free to a good home if it would help; I've never
tried it and it hasn't got a PSU so I don't know what state it's in.

> 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.

Google shows a paper 'High density magnetic recording on a mini flexible
disk drive'
( http://ieeexplore.ieee.org/iel5/20/22848/01061247.pdf )

as possibly mentioning some history of density levels; but the site wants
a sign in.

Dave
-- 
 -----Open up your eyes, open up your mind, open up your code -------   
/ Dr. David Alan Gilbert    | Running GNU/Linux on Alpha,68K| Happy  \ 
\ gro.gilbert @ treblig.org | MIPS,x86,ARM,SPARC,PPC & HPPA | In Hex /
 \ _________________________|_____ http://www.treblig.org   |_______/