Minecraft Alpha level format
Minecraft Alpha level format is a data format used in the Minecraft game, specifically in Java Edition Alpha v1.2.6, and is not used in current versions of the game. It was superceded by the Minecraft Region format and later Minecraft Anvil format. This and other Minecraft formats are extensively documented in the Minecraft Gamepedia wiki.
An alpha level was an entire folder of files including session.lock and level.dat.