Minecraft Science: How Spawners Work - What you need to know to set up a trap around a mob spawner.

Out of date info: it's now a 9x9 area and therefore far easier to setup.

The vast majority of us know how to light up spawners in caves and dungeons to suppress spawning but what most people don't know is what the spawn area is exactly and the restrictions involved.

If you are planning to make an XP farm using a spawner this is step one of the process. Armed with this info you can then get creative but efficient at the same time.