Date   : Mon, 17 Jul 2006 19:47:19 +0100
From   : Philip Pemberton <philpem@...>
Subject: Re: What types of 3.5" Floppy work best with the BBC

Jules Richardson wrote:
> For 5.25" or 3.5"? I hear that 8" units are getting pretty pricey these
 
> days, but I'm surprised there's any shortage of other types resulting i
n 
> high prices.

Maplins still stock 3.5" HD floppy drives - I think they're about =C2£2
0 new, or 
your local computer dealer (yes there are still some of those left) will 
likely be able to sell you one for slightly less than that...

The floppy cable is a bog-standard PC floppy cable. Use the connector bef
ore 
the twist if the drive is jumpered for DS0, use the connector after the t
wist 
if the drive is jumpered for DS1.

> OK, I think you *need* a DSDD unit, don't you? I would have thought tha
t 
> 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.

DSHD is optimised for a data rate of 1Mbit/sec. That's why the Beeb's 
500kbit/sec signal won't work -- the magnetic transitions are just too sl
ow.

Using DSDD (or modded DSHD) discs will change the parameters the drive us
es to 
set up the read/write head, which optimises it for 500kbit/sec. Which is
close 
enough to the Beeb's data rate that the drive will actually work.

You still have to change the step rates though, unless you like the lovel
y, 
grating sound you only get from a 3.5" FDD that's being stepped WAY too s
lowly...

> In which case yes, I can't see you having a problem there - I certainly
 
> added a pair of stock DSDD drives to my Amiga back in the day (I seem t
o 
> recall having to build an interface to do this, but I'm pretty sure tha
t 
> was to get around some quirk in the Amiga side of things, rather than 
> some fundamental "problem" with the use of PC drives)

Aye, but Amigas are just plain weird :P
I seem to recall that rather than update the FDD controller chip (which w
as 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 hac
k.

> You shouldn't need to do that :) You might have to mess around with som
e 
> of the drive jumpers though, so give preference to a drive for which th
e 
> manual's available on the 'net (or jumper info exists in Google's news 
> archive), or failing that a drive which actually labels its jumpers.

The Sony MPF520-E is jumperable, as are the Citizen drives Acorn used in
the 
RiscPC and Archimedes machines.

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...

-- 
Phil.                         | Kitsune: Acorn RiscPC SA202 64M+6G ViewFi
nder
philpem@...                   | Cheetah: Athlon64 3200+ A8VDeluxeV2 512M+
100G
http://www.philpem.me.uk/     | Tiger: Toshiba SatPro4600 Celeron700 256M
+40G