Capacity is how much a container can hold.
Stats
The capacity model is often used with 'life' and 'energy'.
Primary Capacity
The primary capacity is the main amount that something can hold. For example, if a character's health is represented as number between 0 and 100, that range is the primary capacity of the character's health stat.
Over-Filling Primary Capacity
Once the upper-bound of capacity is reached, filling the capacity usually has no further effect.
Extended Capacity
Some games feature an extended capacity in addition to the primary capacity. One example of this is the blue vials in Doom which can charge the player's health past 100. Only the blue vials can do this. Picking up a normal health icon will only fill the player's health to the maximum of it's primary capacity.
Extended capacity normally has an upper limit as well. In Doom, the upper bound of the primary capacity is 100 while the upper bound of the extended capacity is 200.
Reserve Capacity
Reserve capacity takes the form of 'recharge' tanks. These reserve tanks are used to refill the primary capacity. Before they have the capability to do this, they must be charged themselves. Two examples of this are the reserve tanks in the Metriod and Mega Man X series.
Memory Capacity
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Network Capacity
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