Watford DFS


...

9.2 Disc Catalogue

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 bytes.)
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.

Standard DFS will not recognize the second catalogue, and will allow it
to be overwritten.
