mtools: 2m
2.7.3 2m
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The 2m format was originally invented by Ciriaco Garcia de Celis. It
also uses bigger sectors than usual in order to fit more data on the
disk. However, it uses the standard format (18 sectors of 512 bytes
each) on the first cylinder, in order to make these disks easier to
handle by DOS. Indeed this method allows to have a standard sized boot
sector, which contains a description of how the rest of the disk should
be read.
However, the drawback of this is that the first cylinder can hold
less data than the others. Unfortunately, DOS can only handle disks
where each track contains the same amount of data. Thus 2m hides the
fact that the first track contains less data by using a "shadow FAT".
(Usually, DOS stores the FAT in two identical copies, for additional
safety. XDF stores only one copy, but tells DOS that it stores two.
Thus the space that would be taken up by the second FAT copy is saved.)
This also means that you should *never use a 2m disk to store anything
else than a DOS file system*.
Mtools supports these formats only on Linux.
Info Catalog
mtools: bigger sectors
mtools: high capacity formats
mtools: XDF