https://www.theregister.com/on-prem/2021/06/04/fyi-todays-co...

Google and Facebook report a few unreliable CPU cores out of thousands of systems. Meaning maybe a 1/10,000 rate of repeatable CPU errors.

https://www.cs.toronto.edu/~bianca/papers/sigmetrics09.pdf

Google reports 8% of DIMMs being affected by errors. While the differences in metrics prevent comparing the two things directly it seems that DRAM errors are more common than CPU errors.