CHS or LBA translation

[0x3B0]

I only have the MBR of my Hard Disk now I need to know in what sector is the boot sector to read this but I don't know how to find with the CHS. How to find the boot sector through LBA?

[Yoda]

Read an article about MBR structure. http://wiki.osdev.org/MBR
There you'll find details on how to find the boot sector of active partition.

[0x3B0]

I already read this article but it dont explain how to find the boot sector of a partition with the logigal block address or with the cylinder head sector. This is my doubt. I only want to know what I do with the LBA address or with the CHS address because my hard disk have more than 1023 cylinders.

[egos]

Try this.

if "EDD installation check" function is OK:
- use "Extended read" function (42h) with LBA value;
else:
- use "Get disk params" function (8) to get SPT and Heads params;
- translate LBA to CHS using formulas: s = LBA mod SPT + 1, t = LBA div SPT, h = t mod Heads, c = t div Heads;
- check c value (<=1023?);
- use "Legacy read" function (2) with c, h, s values.

[Rudster816]

CHS fields in the MBR are unreliable. Microsoft decided to dump them (rightfully so) when they switched to NTFS, and are using the fields to store something else.

IMO, you shouldn't mess around with CHS at all with HDD's. If the HDD\BIOS doesn't support, sucks for whoever has that 15+ year old machine. Any effort to support CHS will likely be wasted, and could just end up making things worse\introducing bugs. Just my .02 though.

[bluemoon]

I already read this article but it dont explain how to find the boot sector of a partition with the logigal block address or with the cylinder head sector. This is my doubt. I only want to know what I do with the LBA address or with the CHS address because my hard disk have more than 1023 cylinders.

MBR does explains it all.

See the Partition Table article for the format of each partition table entry field.

Follow the link Partition_Table and it explains each field including CHS and LBA of a partiton.

[Yoda]

I do with the LBA address or with the CHS address because my hard disk have more than 1023 cylinders.

Forget about CHS access for any drive larger than 8GiB. Only LBA access will allow you address the whole drive.