@Masato
I have moved your latest posts into this much better matching thread.
By reading the start post of this thread you may get answers to some of your questions.
Here are some notes:
- The size of an Option ROM module depends on its version. Older mainboards may prefer an older Option ROM version, whereas newer mainboard should get a newer (later compiled) Option ROM version.
- The BIOS contains compressed parts. This way it is possible to get a bigger size module inserted without increasing the size of the complete BIOS. A stronger compression compensates the size increase of a certain module.