Block entity

Tile entities are additional data for a block, beyond the block ID and 4 bits of so-called metadata that every block has (as described in the data values article).

The blocks which have tile entities are:
 * Signs, to store the text to be displayed.
 * Chests, Dispensers, and Furnaces, 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.
 * Monster Spawners, to store which mob will be spawned and the time until the next mob is spawned.
 * 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
 * Enchantment Tables for the floating book.
 * Brewing Stands to store the items and brewing time.
 * Air Portals have tile entity data, although it is unknown for what purpose yet.