What is copying garbage collection (stop and copy)? — Heap memory is split into 2 partitions: an old space and a new space. Find live objects by DFS of their reference graph, and move live objects into the new space. The new space is now called the old space. Unreachable objects are simply left in the old space to be overwritten the next time collection occurs. The movement of objects implicitly compacts the objects. Disadvantage: you can only use half of the heap space.