"
Maximum build height has been increased to 256 (was 128)
Empty sections of the world are not loaded into memory
Block ids have been increased to 4096 (was 256) by adding a 4 bit data layer (similar to how meta data is stored)
Block ordering have been changed from x/z/y to y/z/x in order to improve compression
Packets for sending chunks have been updated (a full 128-high chunk is smaller than the old format, and a chunk with lots of empty space is much smaller)
Biomes are saved per x/z column, which means they can be altered by tools"
Sweet