Block entity

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. Block entities are not movable by pistons.

The blocks which have block data are:
 * Signs, to store the text to be displayed.
 * Chests, Trapped Chests, Dispensers, Furnaces, Brewing Stands, Hoppers, Droppers and Beacons 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.
 * 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.
 * Note Blocks, to store which note will be played.
 * Blocks being moved by pistons, to store the offset of block, direction of movement, and ID of moving block.
 * 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 and (if applicable) the player name represented.
 * Command Block, for the command text.
 * Nether Reactor Cores, to store whether the reaction started and the time remaining in the reaction.