General question about dumping current BIOS

[The Gonif]

Hi, back in 2009 I flashed my IP35-e with the beta 18 BIOS, and the system's been stable all this time. Well now I've come across a modded BIOS 18 that enables AHCI (the Southbridge does support it), and I'd like to try that, but first of course I want to back up my current BIOS.

So I did that with the AWDFLASH /pn /sy command, and on a lark did a binary compare of that BIOS with the one I had originally downloaded from this site in 2009... and they didn't match! I then compared it to a BIOS 18 file I had downloaded from Abit.com.tw, and they didn't match either. Finally, I compared the BIOS 18 from Abit with the BIOS 18 from Hexus, and *they* didn't match.

So I guess my question is this: should the BIOS I dumped using AWDFLASH be completely identical to the file that it was originally flashed from two years ago? Changing BIOS settings doesn't affect that, right? And AWDFLASH doesn't store anything in the dumped file like the date you did the dump, does it?

I just want to make sure I have a valid and working backup of the BIOS I'm running before I overwrite it with this other one. It is interesting that my current BIOS doesn't seem to match the original file it came from.

Thanks!

[mhanor]

If it's not too late: take a hex comparision tool (the Total Commander build-in feature should be fine) and you should notice a difference only in the first few hundred bytes (up to 1000h offset, I think).

[The Gonif]

It's not too late -- I've been waiting to hear back from someone before I proceeded.

So wait, why do we expect the BIOSes to differ? When you extract a BIOS into a file, is some metadata added or something?

Thanks for your reply!!

[mhanor]

I'm not sure, but I think that the flash tool makes the BIOS backup from the shadow RAM (a RAM copy of the BIOS). And the difference found at the beggining are some data structures (or part of it) created by the BIOS, at boot.
The true original BIOS should start with 4E 55, continue with some repetitions of 00 00 FE FF, then filled with FF up to offset 1000h. The backup you made should have the same content starting with that offset of 1000h. In which case, you can keep the original and not the backup.