Minecraft wiki entry for Redstone_components, associated text: While not activated, a hopper pulls items from a container above it (or item entities in the space above it) into its own slots and pushes items from its own slots into a container it is facing. Both types of transfers occur every 4 redstone ticks (0.4 seconds), and pushes are processed before pulls. A hopper always pulls items into the leftmost available slot, and pushes items from leftmost slots before rightmost slots (it does not start pushing items from the second slot before the first is empty, from the third slot before the second is empty, etc.).