Date : Tue, 23 Mar 2010 18:20:51 +0000
From : pete@... (Pete Turnbull)
Subject: Re-using floppies
On 23/03/2010 17:02, Jules Richardson wrote:
> Yes, my brain's saying 3.5" DD was 600 oersted and 3.5" HD is around 750 - but
> it's been a while :-)
>
> 5.25" SD/DD was 300 IIRC, and 5.25" HD 600 - so I'd be surprised if they'd
> even format at the wrong density.
Correct.
> 5.25" world further muddied by 77-track drives, 35-track drives, non-Shugart
> drives (Apple etc.), drives that expect disks with hub rings and drives that
> don't (most don't care, thankfully), drives that run at funny speeds, drives
> that are fixed to a specific address etc. :-)
The Apple drives are actually a Shugart mechanism but with Apple's own
analogue electronics. Commodore drives ditto. Then there are Sirius
drives (Victor in the USA) which are variable speed (inner tracks are
used at a higher angular speeds in order that the linear velocity is
more like that at the outer tracks). 5.25" drives exist as 48tpi,
96tpi, and 100tpi versions. In the HD world, some drives are 300rpm (as
the deity intended) while some are 360rpm and some are dual speed
depending on the state of one of the pins (and that may or may not be
linked to the DD/HD write current "density select" pin). Then there are
disks which are soft-sectored, and either 10- or 16-hard-sectored (the
drives don't care about that but the controllers do).
Some early Sony 3.5" drives were also 77-track, but they're also very
rare. More common amongst the early ones are single-sided drives.
There are even drives that don't automatically move the disk shutter.
The earliest 3.5" disks had a latch so you opened the shutter, which
stayed open, to put it in the drive, and when you removed it later, you
pinched the edge to let the shutter close. I still have a few of those.
--
Pete Peter Turnbull
Network Manager
University of York