Minecraft wiki entry for Old, associated text: However, as a result of their limited size, only a few biomes could be generated per world. Also, biomes that were generated here were shrunken 4× (16× area) to allow more biomes to generate. Due to this shrinking, a seed generated different terrain in an old world than in an infinite world, although with similar overall characteristics (for example, the "Island Survival" seed from the seed picker put the player on an island in the middle of the world, but the resemblance ends there).