Description of Physical Layout of 'Perfect' ADFS formats

    Format  g1s0    g1s1    g3      ss      spt     d   sq
Risc OS 2.00:
    L       42      42      57      256     16      2   0
    D       32+271  32+0    90      1024    5       2   0
    E       32+271  32+0    90      1024    5       2   0
Risc OS 2.50:
    F       50      50      90      1024    10      4   2

g1s0 - gap 1 size (in bytes) for side 0 of the disc
g1s1 - gap 1 size (in bytes) for side 1 of the disc
g3 - gap 3 size (in bytes) for both sides of the disc
ss - sector size (in bytes)
spt - sectors per track
d - density:
        1 - single density
        2 - double density
        3 - double+1 density (higher rotation speed deouble density)
        4 - quad density
        8 - octal density
sq - sector skew (in sectors)

Description of the Logical Layout of 'Perfect' ADFS formats

Floppy formats:
    Format  map     zones   directories     Boot block
Risc OS 2.00:
    L       Old     -       Old             No
    D       Old     -       New             No
    E       New     1       New             No
Risc OS 2.50:
    F       New     4       New             Yes

map     information stored      compation required      Recovery story
Old     Free space              Yes                     From directories
New     Space allocation        No                      Two copies stored

directories     Size (entries)  Size (bytes)    Top bit set chars
Old             47              1280            No
New             77              2048            Yes

Boot block - this is a hard disc style feature which has been addopted for
floppy discs for the new, large floppy disc formats. For multi-zone new maps
a boot block is needed to find the map.

Hard disc formats:
    Format  map     Directories     Boot block
    D       Old     New             Yes
    E       New     New             Yes
