Date : Fri, 04 Jun 2004 11:50:07 +0000
From : Jules Richardson <julesrichardsonuk@...>
Subject: Re: 3.5" disk drive
On Fri, 2004-06-04 at 10:30, Jonathan Graham Harston wrote:
> > Message-ID: <EsHyvOOKsJvAFwQH@...>
> > I could be wrong, but I think the extra high-density hole in the disk is
> > used by the drive to determine whether it should spin at 300rpm or 360.
>
> No it doesn't. The hole determines the data rate used, double-density at
> 250kbps or high density at 500kbps. The disk always spins at the same
> rate, 300rpm (incidently, the same a 8" drives). The BBC/Master can only
> use double-density (and single, of course).
Indeed. I believe that's right - speed is always 300rpm for 3.5" media,
whilst it varies for 5.25" depending on density.
Some 5.25" HD drives use one of the pins on the floppy connector to
switch between motor speeds - the Torch Manta board spec mentions both
pin 16 and pin 2 as possibles for this (amongst other things such as
ejecting the disk on some drives, or driving the drive LED). It always
seems a bit hit and miss coupling random 5.25" drives to old equipment,
particularly when no documentation is typically available to cover the
many jumpers normally found on a drive.
> > Have you tried a standard 720k (DD) disk?
>
> You must always use "DD", "blue", "720k", "single hole" disks with BBCs.
> The BBC and Master cannot use "HD", "black", "1.44m", "two hole" disks.
> The A5000 and later can use HD disks.
Presumably to be as reliable as possible, only a double density drive
should be used with the beeb (rather than one capable of accessing high
density disks). Aren't the heads very slightly narrower on a HD drive,
which *may* cause problems if you then use DD media written with a HD
drive in another system? I may well be going mad there, though :-)
Due to the slightly different magnetic properties of DD vs. HD media,
using HD media in a DD drive is also a bad idea. Chances are fair that
it'll work, but not be particularly reliable for long term storage...
cheers
Jules