Cycle-Based Time Model
A time model constructed of repeated unmeasurable chunks, called turns. Each actor typically takes their turn, and then passes control to the next actor in a pre-established order. Turns themselves have no measurable duration or size and they cannot be compared or ordered intrinsicly. However they do have a start and an end, and can be used to measure other phenomena in the model. e.g. an effect that lasts “3 turns” or “until the end of the character’s next turn”.
The turn cycle has no defined start or end where a event can tigger and “turn cycles” cannot be used as a unit of measure. This is the main difference between a cycle-based model and the round-based model.
Diagnostics
Determining if a game is cycle-based or round-based can be difficult because of their high degree of similarity, especially since there is no standard definitions of the terms turn and round in game vocabulary. A game may refer to their rounds as turns (or turns as rounds) and only time spent investigating can determine the truth. Some counter-diagnostics (indicating a round-based model) would include:
- An initiative system that constantly reorders character turns
- The presence of an intentions phase
- The presence of effects, like poison damage, that take place after all actors have taken their turns
- Effects that wear off after a certain number of “turns” but not during a specific actor’s turn
- Essentially, any type of change effect that takes place at a time it is not a specific actor’s turn
Indications
If you have other game mechanics which require there to always be a current player (or character), then a cycle-based model is probably your best choice. This appears to be the case for Magic: The Gathering.
Diagrams
Timing diagram for chess, featuring rounds and sequential resolution of commands via fixed order with immediate action.
Prevalence
Very common in physical board games like chess or checkers and card games like Uno and Magic: The Gathering.