How to code a bootstrap loader

There are many reasons for writing a custom bootstrap program. Most prominent is to achieve an increased understanding of just how a computer operates in its rawest form. Programmers that desire to write their own operating systems will generally utilize custom bootstrap code to load and initialize their system. Utilities that allow users to select different operating systems to run at boot time require a fundamental knowledge of the computer boot sequence. Data recovery services performing digital forensics must understand different bootsector formats in order to restore and read lost data. All of these reasons boil back to understanding the first step a computer makes when powering up - the bootstrap.