The last time I built something like that, it used partition 1 for the current version, 1 for the last version, 1 with the as-shipped version, and 1 that could

The last time I built something like that, it used partition 1 for the current version, 1 for the last version, 1 with the as-shipped version, and 1 that could restore A or B from the internet or USB.