Minecraft wiki entry for History, associated text: Version: 1 byte (may be 0, 2, 3, 4, 5, 6 or 7; the game itself writes 0)
Block IDs: 4kb, 8 bits per block
Block Data: 2kb, 4 bits per block, packed least-significant nybble first
Sky Light: 2kb, 4 bits per block
Block Light: 2kb, 4 bits per block