Does FACTORY RESET also clears/wipes system partition and cache partition?

[AC Question]

I have a new phone which is the Nokia 6, so I want to be prepared before I upgrade to Android Oreo soon, so the question is, does factory reset clears both cache partition and system partition? Like it will be a very clean slate of Android again?

 

[RossJosh]

It does. I think some system partition files are still left intact so it can reset properly, but cached partition will be fully cleaned up. It is a nearly a blank slate. If you want a 100% confirmation, you would have to reflash your ROM.

 

[Rukbat]

The system is left intact. "Factory reset" really means "remove any additions you've made to the phone since it came out of the box". The system and any apps that came in the phone are left alone. (And if you deleted a system app [by rooting], it won't come back.)