Minecraft wiki entry for History, associated text: 1 LevelDB based format
1.1 SubChunkPrefix record (1.0 and 1.2.13 formats)
1.2 LegacyTerrain record (0.9.0 format)
2 0.8.1 and below
2.1 level.dat
2.1.1 NBT Structure
2.2 chunks.dat
2.3 entities.dat
2.3.1 NBT Structure
2.3.2 Entity Format
2.3.3 Mobs
3 References