Harddisk CHS to byte

[misha]

Hi,
1)How do convert C,H,S into bytes.
How can one read in linux if we know the C,H,S.

Also i tried the linear addressing linear = c*H*S + h*S +s -1
.But linear or linear*512 never gave me the exact byte offset to seek.

I am working in linux and using a hexeditor to seek .How many exact
bytes should i seek to find out the extended partition.I read the MBR
and found the exteneded partiton.
00 01 01 00 02 fe 3f 01 3f 00 00 00 43 7d 00 00
80 00 01 02 0b fe bf 7e 82 7d 00 00 3d 26 9c 00
00 00 81 7f 0f fe ff ff bf a3 9c 00 f1 49 c3 01
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

See the third column it is 0f(extended windows).The cylinder is
639(7f81 h)
and sector is 1 .I don't know where to exactly read for the next
partiton.
The byte offset for finding out the next partitions.

If i open hda3(Mind you hda3 is an extended partition on hda) with a
hexeditor i get

00 01 81 7f 83 fe ff 7d 3f 00 00 00 00 82 3e 00
00 00 c1 7e 05 fe ff ff 3f 82 3e 00 7e 04 7d 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

.Now the first partition is of type 83 which is linux and the next
extended partition is of type 05(extended) and cylinder894 and sec1.

*************************************
How do i find the next chain of extended partitions.I mean how do i
convert cylinder 894 ,sec1 and head 0 into absolute bytes so that i
can hexdump the next partition table for finding out ?
************************************

Thank you,
Misha

[Eric Moors]

flup set to cols

> ************************************* How do i find the next chain of
> extended partitions.I mean how do i convert cylinder 894 ,sec1 and head
> 0 into absolute bytes so that i can hexdump the next partition table for
> finding out ? ************************************
>

Try:

sfdisk -l -x -uS /dev/hda

Read sfdisks source.

Eric

[sup...@diydatarecovery.com]

How do i find the next chain of extended partitions.I mean how do i
convert cylinder 894 ,sec1 and head 0 into absolute bytes so that i
can hexdump the next partition table for finding out ?

You shouldn't use CHS values for that, it will limit you to 1024*255*63
equals about 8Gb. Use the LBA start sector instead. Note that most of the
times LBS startsect for 05 is relative to start extended so for the next
EPBR parse start LBA + start extended.

Joep

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