FAT12 is not used for us.

Signed-off-by: cctsao1008 <chiacheng.tsao@gmail.com>
Use assembly code and use instruction SETB, CLRB to get more efficiency.

Signed-off-by: cctsao1008 <chiacheng.tsao@gmail.com>
Re-format header.

Signed-off-by: cctsao1008 <chiacheng.tsao@gmail.com>