it by constructing a gas extraction building on top of a geyser and using worker units to extract the gas from it. In addition, players need to regulate the supplies for their forces to ensure that they can construct the number of units they need. Although the nature of the supply differs between the races—Terrans use physical supplies held in depots, Protoss use psionic energy channeled from their homeworld via pylons, and Zerg are regulated by the number of controlling overlord units present—the supply mechanic essentially works in exactly the same way for each race (just with differing impacts on gameplay), allowing players to create new units when there are sufficient resources to sustain them. Base construction Protoss and Zerg building construction is limited to specific locations: Protoss buildings need to be linked to a power grid, while almost every Zerg structure must be placed on a carpet of biomass, called "creep", that is produced by certain structures. Terran buildings are far less limited, with certain primary base structures possessing the ability to take off and fly slowly to a new location. Terran buildings, however, require the worker unit to continue construction on the building until it is completed. Also, once a Terran building has taken a certain amount of damage, it will catch fire and can eventually burn to the ground without further enemy action if repairs are not performed by a worker unit. The Protoss, by contrast, only require a worker unit to begin the process of transporting a building to the theater of operations via warp, and their buildings' shields (but not their structure) are regenerative. The Zerg worker unit physically transforms into the structure created, which is capable of slowly healing itself. Multiplayer Multiplayer on StarCraft is powered through Blizzard Entertainment's Battle.net Internet service. Through this, a maximum of eight players can compete in a variety of game modes, including simply destroying all other players (which may be competitive, as in Ladder play, or non-ranked, as in melee play), to king of the hill and capture the flag objective-based games. In addition, the game incorporates a variety of specialized scenarios for different types of game, such as simulating a football game, using the Terran hoverbike unit to conduct a bike race, or hosting a Zerg hunting competition. StarCraft is also one of the few games that include a spawn installation, which allows for limited multiplayer. It