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GeoDsp: Images to display the geometry as the BIOS has choosen to
interpret it. Both images are intended to be written to the first ~8MiB
of a raw device (ie /dev/hda, /dev/sda) and be over one large cylinder
of 255*63 512-byte sectors in size.
To save the existing data for restore later:
dd bs=1M iflag=fullblock count=8 if=/dev/sda of=sda.img
GeoDsp1S is a one-sector variant containing all code in one sector that
is intended to test behavior with a typical MBR/partition table layout.
A partition table should be written after writting an image.
GeoDspMS is a multi sector variant intended to look like Syslinux
installed on a file system on the raw device (as opposed to a file
system within a partition).
GeoDspMS can also be used to attempt to make the boot sector look like a
normal file system's boot sector (ie FAT12/FAT16/FAT32). In order to do
this, you must first save a portion the existing boot sector (the
majority of the BIOS parameter block).
dd bs=1 skip=3 count=87 if=/dev/sda1 of=sda1.bpb
dd conv=notrunc if=geodspms.img of=/dev/sda1
dd conv=notrunc bs=1 seek=3 count=87 if=sda1.bpb of=/dev/sda1
dd bs=1 skip=3 count=87 if=/dev/fd0 of=fd0.bpb
dd conv=notrunc if=geodspms.img of=/dev/fd0
dd conv=notrunc bs=1 seek=3 count=87 if=fd0.bpb of=/dev/fd0
Sample output:
CHS 0081,FE,3F
@CHS 0000,01,01:0000003F
@CHS 0001,00,01:00003EC1
@EDD 0000003F:0000003E
@EDD 00003EC1:00003EC1
D=EDD
end
The first line is the interpreted geometry per INT 13h AH=08h,DI=00h (in
hex). The second line is the data value at the sector CHS 0,1,1
(indicating effective sectors per track). The third line is the data
value at CHS 1,0,1 (indicating effective heads per head count). The
fourth line indicates the value read at LBA 63. The fifth line
indicates the value read at LBA 16065. The sixth line indicates the
final expected mode.
Images created by the Perl variant up to and including 6.03 are off by
one and shifted by one byte. In the above, the second line might read
"00003E00" instead of "0000003F".
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