Minecraft wiki entry for Region_file_format, associated text: The Region file format is the binary file format for storing Java Edition chunks from Beta 1.3 to release 1.2. Each file stores groups of 32×32 chunks.[a] The format took the place of the Alpha level format, which had been in use since the Infdev development phase, where chunks were stored in individual files on the file system. The file does not begin with a magic number, unlike other file formats, and begins directly with the header. The format has been superseded by the Anvil file format; however, the Anvil file format made changes only to the chunk format and changed the region file extensions from ".mcr" to ".mca".