Writing MBR

There are different ways for doing that. You can take reference to www.osdev.org for details.

The easy way for me was going with linux and extracting MBR for drives:

1. Backup first

dd if=/dev/sda of=~/[original_bootloader.bin] bs=512 count=1

2. Disassemble the bootloader

ndisasm -b16 -o7C00h ~/[original_bootloader.bin] > ~/[original_bootloader.asm]

3. Make your modifications and reassemble

nasm ~/[original_bootloader.asm] -f bin ~/[modified_bootloader.bin]

4. Overwrite the bootloader

dd if=~/[modified_bootloader.bin] of=/dev/sda bs=512 count=1

‘sda’ is your default primary (bootable) drive. You can modify the .bin file and test in your development enviroment and deploy the successfully edited bootloader  to system.