User blog comment:John Breasly/Minecraft Custom Map/@comment-4099026-20120321231242/@comment-4993782-20120322141107

Actually Law, you could make 256 block tall worlds before the update, but most chose not to unless they had an MAXED OUT Alienware or something for the following reasons:


 * The 2x tall world causes 2x the lag.
 * Giant file sizes = loads of random access memory (RAM).
 * It was a bit buggy.