Spawn chunk

Spawn chunks are chunks found in the world spawn point which are not unloaded from the memory, unlike normal chunks. They are not found in Console Edition. In Pocket Edition, a similar mechanic is called ticking area.

Behavior
Normally, old chunks beyond the render distance get unloaded from the memory, and new chunks get loaded into the memory. Therefore, events like redstone mechanisms and iron golem farms found in old chunks stop processing. Because spawn chunks don't get unloaded, events found in this area continue to process, even if no players are nearby. Be careful when changing the world spawn using, as placing it in a laggy area, such as an area of many redstone clocks, will cause the lag to be present wherever you are in the world.

Other Dimensions
Events in spawn chunks will stop processing after the last player leaves the Overworld for more than 15 seconds, although spawn chunks won't get unloaded.

However, the timer gets reset whenever an entity leaves or enters the Overworld. For example, continuously shooting arrows from dispensers in the Overworld through a nether portal will prevent the events to stop processing, even if no players are in the Overworld.

Processed
The following events will process regardless of player location, as long as it is in spawn chunks:


 * Blocks
 * Water and lava will flow normally.
 * Lava can start fires on nearby flammable objects.
 * Fire will spread to any nearby flammable objects.


 * Entities
 * Dropped items can fall, be moved by water or destroyed by lava, and will despawn after 5 minutes if not picked up by a player or collected by a hopper.
 * Passive mobs, such as baby animals and villagers, can grow into adults.
 * Sheep can eat grass and grow wool.
 * Sand and gravel can fall if the block below is moved or destroyed.
 * Villagers can breed if all conditions are met.
 * Iron golems can spawn inside villages.
 * Primed TNT can fall and explode.
 * If the TNT reaches an unloaded chunk, it will freeze and not explode, therefore, no blocks in the unloaded chunk will be affected, until that chunk is loaded.


 * Mechanisms
 * Minecarts, hoppers, dispensers, and redstone mechanisms will all operate normally.
 * Minecarts can travel around and trigger detector and activator rails.
 * Pistons can extend and retract.

Not Processed
Some events don't get processed until they are in the chunk update range, which varies on the render distance if in singleplayer, and is controlled by an operator in multiplayer, which includes the following:

Blocks
 * Plants (including crops, mushrooms, sugar cane, cacti, and saplings) will not grow.
 * Leaves will not decay.
 * Grass and mycelium will not spread.
 * Ice will not form nor melt.


 * Entities
 * Hostile mobs will instantly despawn if they spawn more than 128 blocks from any player.
 * This includes zombie pigmen at Nether portals and witches in witch huts.
 * They will stand still and will not move if they are more than 32 blocks from any player.
 * Passive mobs will not spawn naturally more than 240 blocks away from a player.
 * The passive mob spawn cap is limited by the number of friendly mobs loaded into memory, which means that any passive mobs present in the spawn chunks count towards the mob cap and will usually prevent friendly mobs from naturally spawning anywhere else in the world.
 * The only exception is when passive mobs spawn as part of a newly generated chunk.

Location
Spawn chunks normally consist of an area of 16x16 chunks in the world spawn point. Entities are only active if all chunks in an area of 5×5 chunks around them are loaded, limiting their activities to an "effective area" of 12×12 chunks around the world spawn point. The exact rule includes chunks whose center is less than or equal to 128 blocks away from the world spawn along both axes. In the rare case where the world spawn is located at the exact center of a chunk, 17 chunks will be loaded along that axis, and 13 of which activate entities.

There are several ways to determine the world spawn point:
 * A compass will always point to the spawn point.
 * The following will only work for players not connected to a bed:
 * In Adventure mode, the northwest corner of the block players spawn on is the world spawn point.
 * In Creative, Spectator, and Survival modes, players spawn on a random block in a 20×20 box centered on the spawn point. The spawn point can be inferred by repeatedly respawning and keeping track of the smallest rectangle encompassing all blocks players have spawned on so far. If the rectangle spans between  on both axes, the spawn point can be on any integer   between   with equal probability. Once the rectangle has grown to 20×20 blocks, the spawn point is in its exact center.
 * Doing the commands then.
 * Entities other than players falling into the exit portal in the End will land on the exact spawn point. Items thrown in will mark the spot in the Overworld. Players will spawn like they normally do, allowing this to be used to perform the above without dying.
 * A new world spawn point can be set using . If no coordinates are provided, the northwest corner of the block the player is currently standing on will become the spawn point. Note that this will not load the new spawn chunks; it merely prevents them from unloading. The chunks can be loaded by walking into range or restarting the server. They will then remain loaded until the spawn point is moved again.
 * Mods or external programs such as NBTExplorer or MCEdit can also be used to find and set the world spawn point.