1 GeoDsp: Images to display the geometry as the BIOS has choosen to
2 interpret it. Both images are intended to be written to the first ~8MiB
3 of a raw device (ie /dev/hda, /dev/sda) and be over one large cylinder
4 of 255*63 512-byte sectors in size.
6 To save the existing data for restore later:
8 dd bs=1M iflag=fullblock count=8 if=/dev/sda of=sda.img
10 GeoDsp1S is a one-sector variant containing all code in one sector that
11 is intended to test behavior with a typical MBR/partition table layout.
12 A partition table should be written after writting an image.
14 GeoDspMS is a multi sector variant intended to look like Syslinux
15 installed on a file system on the raw device (as opposed to a file
16 system within a partition).
18 GeoDspMS can also be used to attempt to make the boot sector look like a
19 normal file system's boot sector (ie FAT12/FAT16/FAT32). In order to do
20 this, you must first save a portion the existing boot sector (the
21 majority of the BIOS parameter block).
23 dd bs=1 skip=3 count=87 if=/dev/sda1 of=sda1.bpb
24 dd conv=notrunc if=geodspms.img of=/dev/sda1
25 dd conv=notrunc bs=1 seek=3 count=87 if=sda1.bpb of=/dev/sda1
27 dd bs=1 skip=3 count=87 if=/dev/fd0 of=fd0.bpb
28 dd conv=notrunc if=geodspms.img of=/dev/fd0
29 dd conv=notrunc bs=1 seek=3 count=87 if=fd0.bpb of=/dev/fd0
35 @CHS 0000,01,01:0000003F
36 @CHS 0001,00,01:00003EC1
37 @EDD 0000003F:0000003E
38 @EDD 00003EC1:00003EC1
42 The first line is the interpreted geometry per INT 13h AH=08h,DI=00h (in
43 hex). The second line is the data value at the sector CHS 0,1,1
44 (indicating effective sectors per track). The third line is the data
45 value at CHS 1,0,1 (indicating effective heads per head count). The
46 fourth line indicates the value read at LBA 63. The fifth line
47 indicates the value read at LBA 16065. The sixth line indicates the
50 Images created by the Perl variant up to and including 6.03 are off by
51 one and shifted by one byte. In the above, the second line might read
52 "00003E00" instead of "0000003F".