AlmaLinux 9 microcode

Question

microcode_ctl-20220207-1.20220510.1.el9_0.noarch.rpm is an AlmaLinux microcode patch RPM package.

What is the difference between BIOS microcode and OS (in this case, AlmaLinux 9) microcode?

Answer 1

Microcode is for the processor (CPU), and it can be delivered either by the firmware (BIOS/UEFI) or by the operating system. Both delivery mechanisms should have essentially the same end result. The updated microcode is not stored persistently within the processor, so it always needs to be re-transmitted to the processor after any time system has been powered off.

Getting a microcode update as part of a firmware update ensures the system will always be running with the updated microcode, as the firmware will feed the microcode to the processor before running any code from any bootable media. But hardware vendors won't always release firmware versions with updated microcode in a timely manner; if a particular hardware model is so old the vendor no longer supports it, they might not provide new firmwares at all. Also, a failed firmware upgrade can brick a system, so there is an element of risk.

To ensure that a new microcode is deployed to as many systems and as quickly as possible, the operating systems can also deliver microcode updates. An OS-level microcode update is also easier to roll back if necessary: just power down the system, boot with a media that does not include the problematic update (if the faulty update causes the processor to become crash-prone or not work at all), delete/downgrade the microcode update package from the installed OS, rebuild initramfs, and reboot.

Answer 2

I understanding about the Microcode! But my question is [What is the different between BIOS microcode and OS microcode?] Can this patch used for BIOS microcode update? "microcode_ctl-20220207-1.20220510.1.el9_0.noarch.rpm"