2.7.1 More sectors

The oldest method of fitting more data on a disk is to use more sectors and more cylinders. Although the standard format uses 80 cylinders and 18 sectors (on a 3 1/2 high density disk), it is possible to use up to 83 cylinders (on most drives) and up to 21 sectors. This method allows to store up to 1743K on a 3 1/2 HD disk. However, 21 sector disks are twice as slow as the standard 18 sector disks because the sectors are packed so close together that we need to interleave them. This problem doesn’t exist for 20 sector formats.

These formats are supported by numerous DOS shareware utilities such as fdformat and vgacopy. In his infinite hubris, Bill Gate$ believed that he invented this, and called it ‘DMF disks’, or ‘Windows formatted disks’. But in reality, it has already existed years before! Mtools supports these formats on Linux, on SunOS and on the DELL Unix PC.