Question How does a motherboard know when a new cpu is installed?

[aerowthefox]

so just a little background is that i work in public IT. its my job to troubleshoot and repair PCs all day long so my knowledge on computers is a little more than the avg gaming joe.

heres the situation:
i just purchased a used asus b550 motherboard off FB market place for a $20 steal. it supposedly 'has bios issues' but it boots to bios fine until i update to the most recent BIOS version. then its just a black screen, monitor turning on to respond to graphical input but nothing displayed, then display powers down and back on with the same black screen in a loop. roll back just a couple bios versions and it boots fine, but then every time it throws a screen saying a new cpu is installed and to hit F1 to setup. now there is a work around in bios to ignore the F1 requirement and that gets me into the OS. so besides the warning its seems to operate fine. however, in addition to the 'bios issue' a capacitor is missing on the board and the bios reads the voltage values as double what they should be. doesnt seem to cause any problems and im guessing the missing capacitor helped the power sensors read accurately.

so what i want to know is as the title says. how does a motherboard know when a new cpu is installed? is the cpu type written to the non-volatile BIOS flash chip? resetting the CMOS settings does not result in a new cpu warning, so logically the information cant be stored in BIOS RAM. what part of this motherboard failing or becoming damaged would result in repeated warnings of a new cpu install? could it be the socket failing to detect the cpu type and defaulting to 'new cpu' everytime?

thanks in advance for the education!!

 

[Lutfij]

The BIOS is what recognizes what is changed in your platform and triggers that message.

 

[dwd999]

Are the cpu's the exact same model, version, etc? Since different cpus have different capabilities the bios would detect those changes. Also now that TPM in cpus has entered the picture the bios would detect that change.

 

[aerowthefox]

i used my own spare 4300g cpu i had lying around. its not from the seller. he said he was upgrading from a 3000 series to a 5950x and thats when it didnt work. it could be that bios doesnt have compatibility but i find that unlikely. most cases when a bios is out of comp the unit doesnt post like mine, but youll have the debug leds flashing between cpu and ram. nothing here. no debug led output at all.

still begs the question why its saying its a new cpu is installed on every boot. corrupted sector on the BIOS flash maybe? i already flashed it back with a compatible bios so it shouldnt be normal software corruption.