Sharding (term)

Sharding is a game design tool created to prevent player overcrowding in outdoor areas of World of Warcraft, and improve server performance.

Behavior
When too many players are in an area, the game automatically creates a new "shard," a copy of that area. Players entering the area will be placed on the new shard. The world appears identical from the player's perspective, with minor differences:
 * Players can only see other players on the same shard.
 * Each shard has its own set of NPCs. As such, rare NPCs may respawn at different times on different shards.
 * Each shard has its own set of objects such as herbs and mining nodes.

Shards can be any geographic size but are usually limited to zones or smaller areas. The borders of a sharded area are invisible to players.

By design, players usually do not notice when the game moves them between shards, but players may notice NPCs momentarily disappear.

Sharding is enabled on all retail World of Warcraft normal realms. Sharding is disabled by default on retail RP realms to facilitate player-run events, but Blizzard occasionally enables it on these realms for server stability when needed.

Sharding and parties
When joining a party or raid party, all party members are automatically moved to the leader's shard, but only if they are in the same zone as the leader. Joining a party, toggling War Mode, and toggling Chromie Time are the only known ways for players to move themselves to a new shard.

Comparison to related tools
Phasing is distinct from sharding. Phasing refers to the changing of the world's appearance to match the player's current progress in the story. For example, the area surrounding Wrathgate appears different depending on whether you've completed the Wrathgate questline. But similar to sharding, players in different phases cannot see each other.

Layering is the same as sharding, but affects an entire realm, covering all zones. Layering was used to alleviate overcrowding at the launch of World of Warcraft Classic, but was later removed.

Cross-realm zones (CRZ) is very similar to sharding, but is designed to prevent under-crowding. If a zone on a realm has very few players, the game automatically moves players from multiple realms into the same "instance" of the zone (effectively a shard) to make it "feel active and alive."