They take up a smaller size of the chip. Which could be seen as an indication that those cores have less caching and less parts for prefetching and stuff like

They take up a smaller size of the chip. Which could be seen as an indication that those cores have less caching and less parts for prefetching and stuff like that. The efficiency core would do less things per cycle but also use less power per cycle. The performance cores would do 3 instructions in a cycle but the efficiency core might only do half an instruction.