Welcome to the dark corner of BIOS reverse engineering, code injection and various modification techniques only deemed by those immensely curious about BIOS

Sunday, February 8, 2009

A Gentle Introduction to BIOS File Structure

The BIOS File Structure in its purest form will look like this:

|        Bootblock          |
|Compressed BIOS components |
The bootblock code responsible for decompression of the compressed BIOS components and to do a very early platform initialization, just enough to make the BIOS decompression process to run flawlessly and to do BIOS recovery procedure in certain bad BIOS flash scenarios. Mind you that not all of BIOS bad flash scenario can be recovered.

As far as I know, BIOS from Award-Phoenix (and its older ancestors Award, Inc. and Phoenix Technologies), AMI BIOS Inc., and all other BIOS vendors use this BIOS file structure. This BIOS file structure maybe used in the binary file of BIOS distributed directly by hardware vendors. However, it's possible that the BIOS distributed by the vendor has been altered in some way in order to do some more sanity checks during the BIOS flashing process. In the latter case, the BIOS file format won't be exactly as shown above, but it will probably compressed, or given some particular information preprended, inserted, or appended into the BIOS binary file distribution.

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