It has been a long time, but I worked on GC at one point. My guess is that it’s the memory footprint (and loss of cache locality) that’s to blame. Copying or ma

It has been a long time, but I worked on GC at one point. My guess is that it’s the memory footprint (and loss of cache locality) that’s to blame. Copying or mark/sweep can be fast, but only if you give them lots of extra memory to accumulate garbage between GC passes. ARC does a little extra CPU work all the time, but it has good locality, and doesn’t need the extra memory.