The Hopper
The hopper is a simple item mover. Every few ticks, it will move 1 item from an inventory above itself into its buffer, and 1 item from its buffer into another inventory. It can output items either down, or sideways. Item entities that fall on top of it will be sucked into the buffer.
A redstone signal will disable the hopper's operation, so it will neither move items nor suck them into its buffer.
Unlike every other item transport mechanism in existence, hoppers will fill the first available slot of an inventory, even if there is another stack where an item would fit.
Workbench.name
Hopper
