Watford DFS

In Watford Electronics DFS there can be either one or two catalogues on
the disc.  They are both in track 0, one occupying sectors 0 and 1, the
other occubying 2 and 3.  The two catalogues are identical in structure:

Sector 00:
00-07 First 8 bytes of the 12 byte disc title
08-0E First filename
0F    Directory of the first filename, top bit set if file is locked
10-1E Second filename
1F    Directory of second filename
.
.
.
Repeated for up to 31 files

Sector 01:
((H) indicates high order two bits of a number that doesn't fit one
or two byes.)
00-03 Last 4 bytes of disc title
04    Count of total number of writes to disc in packed BCD
05    Number of catalogue entries * 8
06    bits 0,1 - number of sectors (H)
      bits 4,5 - !BOOT start option (*OPT4 value)
07    Number of sectors on the disc
08-09 First file's load address (Low byte, High byte)
0A-0B First file's execute address
0C-0D First file's length in bytes
0E    bits 0,1 - First file's start sector (H)
      bits 2,3 - First file's load address (H)
      bits 4,5 - First file's length (H)
      bits 6,7 - First file's start sector (H)
0F    First file's start sector, 8 low bits of a 10 bit number
.
.
.
Repeated for up to 31 files

Sector 02:
This will contain the first file on a 31 file disc.  If this is a 62
file disc then it will contain:
00-07 8 * &AA recognition bytes
08..... As for sector 00

Sector 03:
If this is a 62 file disc:
00-03 5 * nulls
04..... As for sector 01


The disc is recognized as being a 62 file disc by the 8 &AA recognition 
bytes in the disc title area of the second catalogue.  This area would
otherwise be unused.

Non-Watford DFSes will not recognize the second catalogue, and will allow it
to be overwritten.