Hi,

As these bytes are near the string "System Serial Number", I think it is logical to assume that one of them is the serial number, there is also a "System Version" string nearby, so the another one might be an internal version number which might differ from the BIOS version number.

If I had to guess the serial number is the larger block and the version the smaller one.

Obviously this is only conjecture on my part, but it seems logical for these values to be near their description strings.

Interesting I didn’t know the bios contained custom data. But that means that if I flash the bios with a programmer I lose that data? I’ll se if there is a valid SN in that bios.

The serial number is there so they can track if a board gets sent back with an error to know which manufacturing line it was produced. It is encoded into the ROM because then it cannot be as easily tampered with as written text on the board.

Hi, Tony.
I'm not 100% sure, but those little differences could be due to different data stored in DMI tables.

aVd wrote on 2026-05-08, 11:25:

I'm not 100% sure, but those little differences could be due to different data stored in DMI tables.

That is a definite possibility, DMI tables can contain different information, including a serial number. If tony359 uses Linux a utility named dmidecode is most likely available in the distributions package repository and the data can be checked to match.

Hi, @MagefromAntares,
And thanks for confirming my suggestion! I'm keeping too much "useless" information in my mind, so often I'm nor sure, if it's correct 😀

Do you know some useful tool (for Linux, DOS or windows), that can read/write DMI data in BIOS dump files?

aVd wrote on 2026-05-08, 12:36:

Do you know some useful tool (for Linux, DOS or windows), that can read/write DMI data in BIOS dump files?

dmidecode has a command line option --from-dump to specify a file, however I don't know if it works on normal BIOS dumps, it might only work on the dumps made by dmidecode itself (--dump-bin option).

MagefromAntares wrote on 2026-05-08, 12:58:

dmidecode has a command line option --from-dump to specify a file, however I don't know if it works on normal BIOS dumps, it might only work on the dumps made by dmidecode itself (--dump-bin option).

Just tried it with the BIOS dump I need to change some motherboard's serial number, but it can not find any DMI or SMBIOS "entry point", and the DMI table is there. Anyway, thanks for suggestion!

Another possibility is the Ethernet MAC address, which should be different from machine to machine.

EduBat wrote on 2026-05-08, 15:47:

Another possibility is the Ethernet MAC address, which should be different from machine to machine.

Hmm, doubtful. MAC addresses are 6 bytes, and neither of those differing blocks are 6 bytes (one 4 and one 8 bytes). Although, I suppose it's likely that the OUI (i.e. manufacturer prefix) in the first 3 bytes would be constant and not change. But we don't have that either, because in that case there'd be a block of 3 bytes that differed.