As I understand it, the life of an EEPROMs is usually rated at a certain number (e.g. 100k) of writes. Is this "per byte" or writes to the EEPROM system as a whole?
E.g. If the EEPROM has 4k bytes, could I conceivably make 400 million writes if they were evenly distributed?
Specifically, I'm talking about the EEPROM in the Arduino Mega 1280/2560.
Debrief: Thank you stevenvh and Majenko for your helpful explanations. I asked because I wanted to know whether I needed to bother updating only dirty variables when saving a lot of data (a large configuration). From a wear perspective, the answer seems to be 'no': wear happens at the "bit level" and is only caused by setting bits to zero. From a speed perspective, perhaps it would make sense to minimise the size of writes, but if this is not a consideration for your application, then you needn't stress out about it.