A block entity (previously named tile entity) is extra data associated with a block, beyond the block ID and 4 bits of so-called metadata that every block has (as described in the data values article). In addition, block entities are able to perform an action each tick. Block entities are detailed in the chunk format page. A piston cannot move any block entities except its own.
The blocks which have block data are:
- Signs, to store the text.
- Banners, to store the patterns.
- Chests, Trapped Chests, Dispensers, Furnaces, Brewing Stands, Hoppers, and Droppers to store their contents. Furnaces also store the time until the current item is smelted, and the time until the furnace's current fuel item is exhausted. Brewing Stands also store the brewing time. Hoppers also store the time until the next transfer of an item. Chests and Trapped Chests also use the block's position for the opening and closing animation.
- Beacons, to store the pyramid level, active effects, and contents. Also uses the block's position for the beacon beam.
- Monster Spawners, to store which mob will be spawned, additional data about the entity to be spawned (such as position, effects, and entities stacked on top of it), the time until the next mob is spawned, the min and max values for the next spawn delay, and how many mobs to spawn per spawn attempt. Also uses the block's position to display the spinning mob inside.
- Note Blocks, to store which note will be played.
- Piston heads and the blocks they are moving (including indirectly via slime blocks), to store the offset of block, direction of movement, and ID (and data value, if applicable) of the moving block. (A moving block can't be stored as a block because it's not aligned to a grid cell.)
- Jukeboxes, if and which music disc is inside.
- Enchanting Tables, for the floating book.
- End Portals and Ender Chests, for the particle field effect.
- Mob heads, for the type of the head, rotation when placed on top of a block, and (if applicable) data of the player represented.
- Command Block, for the command text, its output strength, and the output text.
- Nether Reactor Cores, to store whether the reaction started and the time remaining in the reaction.
- Daylight Sensor, to force the daylight sensor to update its output signal strength.
- Flower Pots, to show the Block ID and data value of the item displayed inside of it.
- Redstone Comparator, to store its output strength.
- Entities, which are all dynamic, moving objects throughout the Minecraft world, plus several non-moving objects that resemble blocks.