trying to load mbr from sector 2 - windows

Question

i wanted to make a code that will run before the mbr, so i moved the mbr to the second sector, my code to sector zero. in sector 1 I loaded the second sector(which contains the mbr) than i call to address 7c00 to begin the mbr code.
so hard disk looks like this:
sector 0: my program that does IO ans loads sector 1
sector 1: code that loads sector 2
sector 2 mbr code
when i boot i receive this message:
"could not open drive multi 0 disk 0 rdisk 0 partition 1"
its importent to say that i want windows xp to run after my code

Answer 1

What you describe is exactly how the MBR code works:
The MBR of a hard disk is located at the first sector of the hard disk. BIOS will load that sector.
The MBR sector will move itself to some other address and load the first sector of the bootable hard disk partition to address 7C00 (hex). Then it will jump to 7C00 (hex).
However:
The MBR also contains information about the hard disk partitions in the last 80 bytes. If you want to replace the MBR by your own boot sector you'll have to copy the data located in the last 80 bytes. Otherwise hard disk access won't work any longer because the OS will look for hard disk information in thes last 80 bytes of the first sector of the hard disk.
If you want to replace the boot sector of the bootable partition you have a similar problem. Depending on the file system used there is file system information stored in some bytes of the boot sector. For FAT or NTFS the first three bytes must be a "JMP" instruction and the following about 65 bytes contain file system information.