Date   : Thu, 13 Oct 2005 11:49:22 +0100
From   : "David Hunt" <dm.hunt@...>
Subject: Re: 3.5" Floppy For A Master

Yes there is!

A High Density (HD) drive has a finer gap head that is driven with lower
power than Double Density (DD). This allows a finer pitch of sectors when
combined with high sensitivity, fine magnetic particles such as the surface
of an HD disc.
 
A weaker head field reduces crosstalk into nearby data, thus improving
stability on discs that have portions that are frequently accessed.

So to cut a long story short, if you cover the Media Sense hole to fake DD,
you will be trying to use an HD disc in a DD drive - i.e. your data won't be
there next time you read it! The same applies to using HD 5.25" discs in a
DD or (Single Density) SD floppy drive.

BTW: if you are trying to connect a PC floppy to a Beeb, make sure the MS
jumper is fitted to the floppy otherwise the sector frequency will be preset
to HD and the Beeb just can't deal with it.

I've had more joy with DD drives than HD drives, a couple more jumpers
needed to be changed on Sony and Mitsubishi drives (1990-1995 vintage) that
required the drive to be partially dismantled to get at them!

Dave ;)

-----Original Message-----
From: Majordomo List Manager [mailto:majordomo@...] On Behalf Of
Jonathan Graham Harston
Sent: 12 October 2005 23:03
To: bbc-micro@...
Subject: [BBC-Micro] Re: 3.5" Floppy For A Master

Eelco Huininga <eelco@...> wrote:
> Is that a DD or HD drive?
 
In practice there's no such thing.
 
A 3.5" drive detects the disk type by noticing the second hold on
a HD disk. That's one of the reasons you shouldn't fake a HD disk
to DD by covering the hole, 'cos the drive will then use the wrong
write current to write to the disk and ruin it.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
BBC IDE Hard Drive Interface - http://mdfs.net/Info/Comp/BBC/IDE