Date   : Mon, 09 Feb 2004 17:11:17 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: Discs

> Disc drives themselves come in different flavours too. PC 5.25" floppy
> drives generally don't work with BBC discs, although they can be used, they
> have a different track stepping,

For clarity, you presumably mean that standard PC disk formats use a
different geometry (sector size, tracks, sectors per track etc.) when
formatted on a PC using a *standard* format utility? The physical floppy
*drive* hardware is the same, and assuming you get an necessary jumpers
set up correctly, a drive sourced from a PC will work with a BBC.

Caveat - I'm not sure about the 40/80 track switching for reading a 40
track disk in an 80 track drive. For a couple of the Watford drives I
have, it seems extra circuitry was added to stock drives to (presumably)
double-step the heads in hardware when the drive was selected as a 40
track unit. I guess the floppy controller IC in the BBC just doesn't
have the ability to do this under software control?

> BBC Disc drives are 40-track, 80-track or 40/80 switchable. Some will claim
> there is no such thing as an 80-track only drive, but I have seen them and
> can confirm the existence of these bizarre units. 

See above; aren't those standard high-density floppy drives without any
double-stepping logic on the drives themselves? i.e. they're the norm as
far as the world of floppy drives as a whole is concerned; the oddities
are the 40/80 hardware-switchable drives which are perculiar to just the
BBC. Maybe I just totally confused myself (and everyone else :-)

> There are also some propietary disc formats around as a result of
> third-party DFSes. One in particular is the Watford DDFS, which uses a DFS
> disc structure, but in Double Density mode. I have no idea what the exact
> capacity of this format is, but it is larger than the average 100K/200K DFS
> disc.

An ex-Torch chap was speculating the other day that the Watford format
just happens to be the same as the Torch format by the way, although I'm
yet to verify that. So in theory a Watford DDFS ROM will also read Torch
floppies.

cheers

Jules