Re: where does grub put the MBR?
On Thu, May 04, 2006 at 04:16:08PM -0500, Nate Bargmann wrote:
> * Alvin Oga <aoga@mail.Linux-Consulting.com> [2006 May 03 07:06 -0500]:
>
> > > > Well the MBR, is always in the same place. It is *always* the first 512
> > > > bytes on the physical disk.
> >
> > the MBR is the first 446 bytes of each partition ....
> > 16 bytes for each of the 4 primary partition
> > 2 bytes for the boot flag
> >
> > and if you have more than one partition, the "boot record" is the
> > first 448 bytes of each primary primary
>
> So, the MBR (first 512 octets) contains the partition information for
> up to four primary partitions or one to three primaries and one extended.
> Where are succeeding partition (hda5 and higher) records kept for
> partitions in an extended partition?
In the extended partitions themselves. The extended partition has its
own MBR which contains two partitions entries - one for a logical
partition, and the second for another 'extended partition' which
repeats the process.
Hence there is no limit to the number of logical partitions, but if a
logical partition is corrupted, you lose all of the partitions which follow.
This is the output of a program I wrote some time ago to display all of
the partitioning information on my drives:
[LILO] Master Boot Record 00000000:00000000
[MWIN] Part 0: 00 01-000-01 06 fe-0c2-3f 0000003f 3132612 (DOS 16-bit >=32)
[BSDI] Part 1: 00 00-0c3-01 9f fe-185-3f 002fcd03 3132675 (BSD/OS)
Part 2: 00 00-186-01 83 fe-247-3f 005f9a06 3116610 (Linux native)
Part 3: 00 00-248-01 05 fe-3ff-3f 008f2848 146914425 (Extended)
Master Boot Record 00000000:008f2848
[MWIN] Part 0: 00 01-248-01 06 fe-287-3f 0000003f 1028097 (DOS 16-bit >=32)
Part 1: 00 00-288-01 05 fe-298-3f 000fb040 273105 (Extended)
Master Boot Record 000fb040:008f2848
[LILO] Part 0: 00 01-288-01 83 fe-298-3f 0000003f 273042 (Linux native)
Part 1: 00 00-299-01 05 fe-2a6-3f 0013db11 224910 (Extended)
Master Boot Record 0013db11:008f2848
Part 0: 00 01-299-01 82 fe-2a6-3f 0000003f 224847 (Linux swap)
Part 1: 00 00-2a7-01 05 fe-3ac-3f 0017499f 4209030 (Extended)
Master Boot Record 0017499f:008f2848
Part 0: 00 01-2a7-01 83 fe-3ac-3f 0000003f 4208967 (Linux native)
.
.
.
The bracketed information on the left identifies the type of boot
code found in the first sector of the partition.
Regards,
DigbyT
--
Digby R. S. Tarvin digbyt(at)digbyt.com
http://www.digbyt.com
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