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

You could look into GRUB. I am by no means an expert at MBR code and it's been a long while since I ran a *nix OS, but I remember that the bootloader worked in stages and loaded the stages from the disk before the OS started. You could write your own stage to do the work you need done before the OS loads and then boot the OS. I'm not sure how practical this option is, particularly since the code seems to be in the middle of a rewrite because the "legacy" version was unmaintainable according to the documentation.