No, the GC still periodically runs, polluting cache, consuming cycles and halting the rest of the program until it's done. The only exception is if you complete

No, the GC still periodically runs, polluting cache, consuming cycles and halting the rest of the program until it's done. The only exception is if you completely avoid allocations, which is generally next to impossible in GC based languages. With ARC, there is exactly zero overhead unless a new reference is created or destroyed. In that case there's an integer add or subtract, not a global "stop the world" kind of event.