mtools: 2m

1 
1 2.7.3 2m
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1 
1 The 2m format was originally invented by Ciriaco Garcia de Celis. It
1 also uses bigger sectors than usual in order to fit more data on the
1 disk.  However, it uses the standard format (18 sectors of 512 bytes
1 each) on the first cylinder, in order to make these disks easier to
1 handle by DOS. Indeed this method allows to have a standard sized boot
1 sector, which contains a description of how the rest of the disk should
1 be read.
1 
1    However, the drawback of this is that the first cylinder can hold
1 less data than the others. Unfortunately, DOS can only handle disks
1 where each track contains the same amount of data. Thus 2m hides the
1 fact that the first track contains less data by using a "shadow FAT".
1 (Usually, DOS stores the FAT in two identical copies, for additional
1 safety.  XDF stores only one copy, but tells DOS that it stores two.
1 Thus the space that would be taken up by the second FAT copy is saved.)
1 This also means that you should *never use a 2m disk to store anything
1 else than a DOS file system*.
1 
1    Mtools supports these formats only on Linux.
1