I've read that current CPUs have more than a hundred million transistors per square millimeter. I can't imagine that every single one of those works perfectly and will stay working perfectly for the entire lifetime of the CPU.
How do we design CPUs that don't die or stop working properly when one out of a hundred million transistors fails?
The difference between CPUs actually may not be due to different designs - but due to manufacturing errors. Intel for example might have a production line only for "tier 1" processors (e.g. i7) but during manufacturing, some of the transistors, for some reason, fail to function. During quality tests they can check which transistors fail and reprogram the microcode to use only the good transistors. Then you end up with a lower tier processor (e.g. i5, i3)
Lots of really good information here: https://www.google.com/amp/s/www.techspot.com/amp/article/18...