$ dd if=boot.img of=boot.BPB.img bs=512 count=1
1+0 records in
1+0 records out
512 bytes copied, 0.0129819 s, 39.4 kB/s
$ od -c boot.BPB.img 
0000000 353   < 220   m   k   f   s   .   f   a   t  \0 002 020 001  \0
0000020 002  \0 002  \0  \0 370      \0   ?  \0 377  \0  \0  \0  \0  \0
0000040  \0 340 001  \0 200 001   ) 351   Q 376 004   b   o   o   t    
0000060                           F   A   T   1   6             016 037
0000100 276   [   | 254   " 300   t  \v   V 264 016 273  \a  \0 315 020
0000120   ^ 353 360   2 344 315 026 315 031 353 376   T   h   i   s    
0000140   i   s       n   o   t       a       b   o   o   t   a   b   l
0000160   e       d   i   s   k   .           P   l   e   a   s   e    
0000200   i   n   s   e   r   t       a       b   o   o   t   a   b   l
0000220   e       f   l   o   p   p   y       a   n   d  \r  \n   p   r
0000240   e   s   s       a   n   y       k   e   y       t   o       t
0000260   r   y       a   g   a   i   n       .   .   .      \r  \n  \0
0000300  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0000760  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0   U 252
0001000
$ od -A d -j 11 -N 2 -t d2 boot.BPB.img 
0000011    512
0000013
$ BPB_BytsPerSec=512
$ od -A d -j 13 -N 1 -t d1 boot.BPB.img 
0000013   16
0000014
$ BPB_SecPerClus=16
$ echo $(( $BPB_BytsPerSec * $BPB_SecPerClus ))
8192
$ od -A d -j 14 -N 2 -t d2 boot.BPB.img 
0000014      1
0000016
$ BPB_RsvdSecCnt=1
$ od -A d -j 16 -N 1 -t d2 boot.BPB.img 
0000016      2
0000017
$ BPB_NumFATs=2
$ od -A d -j 17 -N 2 -t d2 boot.BPB.img 
0000017    512
0000019
$ BPB_RootEntCnt=512
$ od -A d -j 19 -N 2 -t d2 boot.BPB.img 
0000019      0
0000021
$ od -A d -j 32 -N 4 -t d4 boot.BPB.img 
0000032      122880
0000036
$ BPB_TotSec16=0
$ BPB_TotSec32=122880
$ TotSec=$BPB_TotSec32
$ echo $TotSec
122880
$ echo $(( $TotSec * 512 ))
62914560
$ ls -l boot.img 
-rw-r--r-- 4 brock users 62914560 Feb 19  2017 boot.img
$ RootDirSectors=$(( ( ( $BPB_RootEntCnt * 32 ) + ( $BPB_BytsPerSec - 1 ) ) / $BPB_BytsPerSec ))
$ echo $RootDirSectors
32
$ od -A d -j 22 -N 2 -t d2 boot.BPB.img
0000022     32
0000024
$ BPB_FATSz16=32
$ FATSz=$BPB_FATSz16
$ FirstDataSector=$(( $BPB_RsvdSecCnt + ( $BPB_NumFATs * $FATSz ) + $RootDirSectors ))
$ echo $FirstDataSector
97
$ DataSec=$(( $TotSec - ( $BPB_RsvdSecCnt + ( $BPB_NumFATs * $FATSz ) + $RootDirSectors ) ))
$ echo $DataSec
122783
$ CountofClusters=$(( $DataSec / $BPB_SecPerClus ))
$ echo $CountofClusters
7673
$ rootDirStart=$(( $BPB_RsvdSecCnt + $BPB_NumFATs * $FATSz ))
$ echo $rootDirStart
65
$ echo $RootDirSectors
32
$ dd if=boot.img of=FAT.img bs=512 count=$FATSz skip=$BPB_RsvdSecCnt
32+0 records in
32+0 records out
16384 bytes (16 kB, 16 KiB) copied, 0.00806627 s, 2.0 MB/s
$ dd if=boot.img of=boot.rootdir.img bs=512 count=$RootDirSectors skip=$rootDirStart
32+0 records in
32+0 records out
16384 bytes (16 kB, 16 KiB) copied, 0.00591393 s, 2.8 MB/s
$ od -A d -t a boot.rootdir.img
................
0000800   A   C nul   O nul   P nul   Y nul   I nul  si nul dc2   N nul
0000816   G nul   . nul   l nul   i nul   n nul nul nul   u nul   x nul
0000832   C   O   P   Y   I   N   ~   1   L   I   N  sp nul nul   & can
0000848   S   J   S   J nul nul   & can   S   J   [ dle enq   I nul nul
................
0000928   A   c nul   m nul   d nul   l nul   i nul  si nul  si   n nul
0000944   e nul   . nul   t nul   x nul   t nul nul nul nul nul del del
0000960   C   M   D   L   I   N   E  sp   T   X   T  sp nul nul  si etb
0000976   S   J   S   J nul nul  si etb   S   J enq nul  bs nul nul nul
................
0002112 nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
*
0016384
$ od -A d -j 800 -N 64 -t a boot.rootdir.img 
0000800   A   C nul   O nul   P nul   Y nul   I nul  si nul dc2   N nul
0000816   G nul   . nul   l nul   i nul   n nul nul nul   u nul   x nul
0000832   C   O   P   Y   I   N   ~   1   L   I   N  sp nul nul   & can
0000848   S   J   S   J nul nul   & can   S   J   [ dle enq   I nul nul
0000864
$ dd if=boot.rootdir.img of=Copying.linux.direntry bs=1 skip=832 count=32
32+0 records in
32+0 records out
32 bytes copied, 0.00852023 s, 3.8 kB/s
$ od -A d -t a Copying.linux.direntry 
0000000   C   O   P   Y   I   N   ~   1   L   I   N  sp nul nul   & can
0000016   S   J   S   J nul nul   & can   S   J   [ dle enq   I nul nul
0000032
$ od -A d -j 26 -N 2 -t d2 Copying.linux.direntry 
0000026   4187
0000028
$ CLUSTERADD0=4187
$ echo $(( $CLUSTERADD0 * 2 ))
8374
$ od -A d -j 8374 -N 32 -t d2 FAT.img 
0008374   4188   4189     -1   4191   4192   4193   4194   4195
0008390   4196     -1     -1     -1     -1     -1     -1     -1
0008406
$ od -A d -j $(( 4187 * 2 )) -N 2 -t d2 FAT.img
0008374   4188
0008376
$ od -A d -j $(( 4188 * 2 )) -N 2 -t d2 FAT.img
0008376   4189
0008378
$ od -A d -j $(( 4189 * 2 )) -N 2 -t d2 FAT.img
0008378     -1
0008380
$ CLUSTERADD0=4187
$ CLUSTERADD1=4188
$ CLUSTERADD2=4189
$ od -A d -j 28 -N 4 -t d4 Copying.linux.direntry 
0000028       18693
0000032
$ FILESIZE=18693
$ echo $FirstDataSector
97
$ echo $BPB_SecPerClus
16
$ function DataCluster2Sector()
{
   local result=$(( ( ( $1 - 2 ) * $BPB_SecPerClus ) + $FirstDataSector ))
   echo "$result"
}
$ SECTORADD0=`DataCluster2Sector $CLUSTERADD0`
$ SECTORADD1=`DataCluster2Sector $CLUSTERADD1`
$ SECTORADD2=`DataCluster2Sector $CLUSTERADD2`
$ echo $SECTORADD0 $SECTORADD1 $SECTORADD2
67057 67073 67089
$ dd if=boot.img bs=512 skip=$SECTORADD0 count=16 of=copying.LINUX-0
16+0 records in
16+0 records out
8192 bytes (8.2 kB, 8.0 KiB) copied, 0.00293192 s, 2.8 MB/s
$ dd if=boot.img bs=512 skip=$SECTORADD1 count=16 of=copying.LINUX-1
16+0 records in
16+0 records out
8192 bytes (8.2 kB, 8.0 KiB) copied, 0.00790882 s, 1.0 MB/s
$ dd if=boot.img bs=512 skip=$SECTORADD2 count=16 of=copying.LINUX-2
16+0 records in
16+0 records out
8192 bytes (8.2 kB, 8.0 KiB) copied, 0.00899374 s, 911 kB/s
$ cat copying.LINUX-* > copying.LINUX-all
$ dd if=copying.LINUX-all bs=$FILESIZE count=1 of=copying.LINUX
1+0 records in
1+0 records out
18693 bytes (19 kB, 18 KiB) copied, 0.00840871 s, 2.2 MB/s
$ head copying.LINUX

   NOTE! This copyright does *not* cover user programs that use kernel
 services by normal system calls - this is merely considered normal use
 of the kernel, and does *not* fall under the heading of "derived work".
 Also note that the GPL below is copyrighted by the Free Software
 Foundation, but the instance of code that it refers to (the Linux
 kernel) is copyrighted by me and others who actually wrote it.

 Also note that the only valid version of the GPL as far as the kernel
 is concerned is _this_ particular version of the license (ie v2, not
$ tail copying.LINUX
  `Gnomovision' (which makes passes at compilers) written by James Hacker.

  <signature of Ty Coon>, 1 April 1989
  Ty Coon, President of Vice

This General Public License does not permit incorporating your program into
proprietary programs.  If your program is a subroutine library, you may
consider it more useful to permit linking proprietary applications with the
library.  If this is what you want to do, use the GNU Library General
Public License instead of this License.