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primary and extended partition info are read i.e C drive is found how to find other drives. I am not able to interpret Extended partition information (no docs in my hand). Like to have some pointers to good docs.

IIRC, the first sector of the extended partition just has another MBR which you read to find the partitions.

I am using Acronis Disk Editor Demo and it gives different CHS value for other drives. It shows a Fat32 drive and it shows another drive as REAL/32 big. First of all it's boot signature is not 0AA55h but 0702Ah. If you say it's another MBR then it's signature should also be 0AA55h. Is my MBR scrambled? i don't think so because it boots properly. Other possibility is that i am misinterpreting. But i double checked everything

Try calculating the offset from the start of the extended partition. Also, stop using the CHS values!. LBA values are better in that they work on big disks (which is nowadays, pretty much, any disk > 8GB) whereas CHS doesn't. Try searching the forum for more help, there is most certainly more available. I recall helping somebody read extended partition table entries less than a week ago.

@candy : Try calculating the offset from the start of the extended partition. Also, stop using the CHS values!.

Both these mistakes are done by me. I used CHS value to read from Hard Disk and found that head value shouldn't be more than 15. More than five hours spent for debugging this code and finally learnt the lesson.
A hard lesson learnt today is,

use LBA everywhere.