The BIOS update that made two hard drives disappear
After a routine motherboard firmware update, two drives vanished from Windows. Rolling back didn't help. A CMOS clear did.
The problem
I updated the BIOS on my main PC (an ASRock B450 Pro4). Afterwards, the two drives on the board's extra SATA ports (A1 and A2) were gone from Windows. These two ports run on a separate ASMedia chip, not the main chipset.
Device Manager showed that chip either missing completely, or present in the old IDE mode with error Code 12 ("not enough free resources").
What I ruled out
- Cables and drives: the BIOS setup screen could still see both drives.
- Windows: no driver installs or Windows updates around the time it broke, and no hardware errors in the logs.
- The new BIOS version itself: I flashed back to the previous version. The drives stayed missing.
- Obvious settings: CSM, Fast Boot, SATA Hot Plug, the controller's own setting, and Windows PCIe power saving. None of them changed anything.
The clue
Windows' device history showed that, before the update, the chip came up in AHCI mode with the board maker's ID on every single boot. After the update it never did. That meant the BIOS was no longer setting the chip up during startup. That's a stored-state problem, not a version problem.
I also decoded the BIOS's own menu definitions with two open-source tools (UEFIExtract and IFRExtractor) to see every setting and its true factory default, including hidden ones.
The fix
A full CMOS clear: power off at the wall, short the CLRCMOS jumper, then set the few required settings again. On the second boot after the clear, the BIOS listed both drives, and Windows got the chip in the correct mode.
"Load defaults" and flashing back don't wipe everything the firmware stores. A CMOS clear does.
What I changed so it doesn't happen again
- A BIOS-update checklist that now includes "clear CMOS right after flashing".
- I moved the backup drive off that extra chip onto the main chipset ports, and I'm replacing the chip with a dedicated SATA card.