Date   : Mon, 17 Jul 2006 20:06:46 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: What types of 3.5" Floppy work best with the BBC

Philip Pemberton wrote:
>> OK, I think you *need* a DSDD unit, don't you? I would have thought 
>> that the beeb can't cope with the data rate needed for a DSHD drive.
> 
> Half right.
> 
> You CAN use a DSHD drive - in fact, I use one on my Master 128. You just 
> have to either use DSDD discs or cover the "disk type" hole on any DSHD 
> disks you use.

Don't you get data reliability problems though, even if using DD media? Isn't 
the head physically different? I'm sure there are documented problems - ISTR 
particularly if you format/write a DD disk in a HD drive and then subsequently 
try and read it in a true DD drive. To maintain compatibility it's best to use 
a real DD drive, but if using a HD drive you can usually "get away with it".

[Amigas]
> I seem to recall that rather than update the FDD controller chip (which 
> was a custom part) to support DSHD, they added another I/O line to the 
> floppy connector and made the drive spin at half speed instead. What a 
> nasty hack.

I seem to recall doing something with a flip-flop IC sitting between the drive 
and the Amiga, but I can't for the life of me remember what it was now... back 
then 'real' external Amiga drives were still running at 50 pounds or so each, 
but you could lash something up with about a pound's worth of electronics and 
a 5 quid PC drive...

> No, I'm NOT advocating anyone steal a floppy drive out of a RiscPC to 
> run on their Beeb, RiscPC spares are expensive enough as it is...

I'm starting to realise that - think I'm going to sell my StrongARM RPC and 
the Hydra as I'll never get around to doing anything useful with them! Just 
trying to make sense of EBay today and it's downright horrible :-)

cheers

Jules
(currently trying to bash some life into the System Three)