je to tak jak rika Jarda, ten dd nema mazat boot sector a partition table, ale zacatek te dosove partition, zde pro zvydave cast man fdisk:
DOS 6.x WARNING
       The DOS 6.x FORMAT command looks for some information in the first sector of the data area  of  the
       partition,  and  treats this information as more reliable than the information in the partition ta‐
       ble.  DOS FORMAT expects DOS FDISK to clear the first 512 bytes of the data  area  of  a  partition
       whenever  a size change occurs.  DOS FORMAT will look at this extra information even if the /U flag
       is given -- we consider this a bug in DOS FORMAT and DOS FDISK.
       The bottom line is that if you use cfdisk or fdisk to change the size  of  a  DOS  partition  table
       entry,  then  you  must  also use dd to zero the first 512 bytes of that partition before using DOS
       FORMAT to format the partition.  For example, if you were using cfdisk to make a DOS partition  ta‐
       ble entry for /dev/sda1, then (after exiting fdisk or cfdisk and rebooting Linux so that the parti‐
       tion table information is valid) you would use the command  "dd  if=/dev/zero  of=/dev/sda1  bs=512
       count=1" to zero the first 512 bytes of the partition.