On Dec 26, 14:35, Nico de Jong wrote:
> I've had a look at the floppy formats supported by my conversion
system,
> which btw originates in the UK. I havnt come across BBC formats in
the
> servicebureay, but according to the software BBC is found in quite
some
> flavours, reaching from single-side single-density 5.25" to DSDD 3.5"
> Before you spend a lot of time playing around with things, it would
be good
> to know the discs physicals and logicals.
The single-density "DFS" format is particularly easy. It consists of
10 sectors of 256 bytes per track, numbered 0 to 9, and is nominally
single-sided. If you have doubled-sided drives, side 0 of the first
drive is referred to as drive 0, and the sector headers are just as
you'd expect; the second side (side 1) is referred to as drive 2, and
has the *same* sector headers (ie the "head" number is stored in the
header as "0", not "1"). Drives can be either 40-track or 80-track;
the only difference (apart from the number of tracks, obviously) is the
size stored in the directory. Recording method is standard FM with an
Index Mark. There's no sector-to-sector interleave on a track, but the
start of each track is skewed by three sectors, compared to the
previous one.
The directory occupies the first two sectors of track 0, and is
extremely simple. I can describe it if you like, or give you a 512-byte
dump of the two sectors.
The double-density "ADFS" format is a bit more complicated. There are
several variations, but the BBC Micro (as opposed to the later
Archimedes) supported "S" (small) format (40 track SS), "M" (medium)
(40 track DS or 80 track SS), and "L" (80 track DS). The DS versions
are a little unusual in that they use all of side 0 before using any of
side 1, but the head numbers are what you'd expect (ie "0" for side 0
and "1" for side 1). Each track is 16 sectors of 256 bytes, numbered
0-15, no interleave, track-to-track skew of 9 (ie track one begins with
sector 9, track 1 begins with 2, track 2 with 11, etc), standard MFM
but normally *without* an Index Mark (though it shouldn't matter if you
put one in).
The directory's a bit more complicated becasue there's a proper free
space map, and it's a hierarchical structure.
--
Pete Peter Turnbull
Network Manager
University of York
Received on Fri Dec 26 2003 - 10:36:04 GMT