Write MBR Code

Question

I am an electrical engineer who has recently discovered the need to modify the code in the MBR. Basically I need the ability to execute code on the HDD before, the OS starts up

Answer 1

The editing of the MBR is perfectly possible from within Windows(XP). For this is used the HxD hex editor, you can literily copy-paste a hex file over the MBR, even on your active system drive (use with caution ! :)) http://mh-nexus.de/en/hxd/

As a starting point a would get the MBR of which the source is available, for instance Grub. (So let grub do the botoing to Windows) With this you have a good starting point to do the changes to your MBR. Editing the MBR shouldn't be too hard, as this little piece of software is pretty basic. Some 16bit (DOS) assembler skills are needed though. An other way is to let grub run some extra payload and not changing the MBR at all, but I'm 100% sure if this is possible; please refer to Grub manuals.