Chunk format/McRegion

Chunks store the terrain and entities within a 16x16x128 area. They also store precomputed lighting, heightmap data for Minecraft's performance and other meta information.

Chunks were first introduced in Minecraft Infdev. Before the addition of the region file format in Beta 1.3, chunks were stored as individual chunk files. The file names contained the chunk's position encoded in Base36 and the extension ".dat".

The Data, SkyLight, and BlockLight are arrays of 4-bit values. The low bits of the first byte of one of these corresponds to the first block in the Blocks array.