Horst wrote,
>Q1: is the stuff after the MBR and below 7E00 hex the partition table ?
The partition table is in that area, near the beginning.
You should find the partition table starting at 0x1C0 and ending at 0x1FF
from the beginning of the drive. There are four entries, each 16 (decimal)
bytes long.
Before the partition table is the MBR. After the partition table is junk,
up until the beginning of the first partition.
Note that the space from 0 through 0x7E00 occupies exactly 63 (512-byte)
sectors. If you do "fdisk -l /dev/hdX", it will probably report that
your drive has 63 sectors per track. This is not a coincidence--most
partitioning software likes to begin partitions at the beginning of a
track. The long stretches of 0's that you saw are the empty space that
fdisk left in order to move the start of the first partition to the
beginning of the first track after the MBR.
Also note that unless you have a very old drive, your actual physical
tracks are probably not 63 sectors long...that's just a little white lie
the BIOS tells in order to make the sector number fit in the appropriate
MS-DOS data structures.
In MS-DOS parlance, the MBR and the extra 0 sectors are called "hidden
sectors".
>Q2: if I'd just have a dd dump of some partition hdXN (like hdb1)
>how useful would this be if I try to restore it to another device?
> (assuming that one has enough space)
I only recommend this if you restore to a partition that's the same size
as the original parition.
If you restore to a partition that's too small, the danger is obvious.
If you restore to a partition that's too large, the restored partition may
mount OK, but you'd only be able to access the restored size...the rest of
the space would be unavailable.
Note that some filesystems (including FAT12/16/32) store info about the drive's
geometry as part of the superblock. I don't think Linux pays any
attention to this information, but if you restore to a drive with a
geometry that's very different from the original, other OS's (e.g. MS-DOS)
may not like it.
- Neil Parker
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