Jonathan de Boyne Pollard wrote some reasonably concise descriptions of this and related issues. His overall "FGA" index is at [1], and you might be more specif

Jonathan de Boyne Pollard wrote some reasonably concise descriptions of this and related issues. His overall "FGA" index is at [1], and you might be more specifically interested in [2] and [3]. [1] http://jdebp.uk./FGA/ http://jdebp.uk./FGA/ [2] http://jdebp.uk./FGA/pcat-boot-process.html http://jdebp.uk./FGA/pcat-boot-process.html [3] http://jdebp.uk./FGA/efi-boot-process.html http://jdebp.uk./FGA/efi-boot-process.html