The "Active Time Battle" system was introduced by Hiroyuki Ito in Final Fantasy IV (1991). In this system, time-keeping does not stop at the end of a turn. Instead, each character has an ATB meter that gradually fills over time in real time, and players must think and act quickly lest they miss their chance to take their turn. Once filled, the player is allowed to issue a command for that character. The fact that enemies can attack or be attacked at any time is credited with injecting urgency and excitement into the combat system. The ATB system was fully developed in Final Fantasy V (1992), which improved it by introducing a time gauge to indicate to the player which character's turn is next. The ATB system has since been used in nearly all later Final Fantasy role-playing video games up until Final Fantasy X (2001), after which subsequent Final Fantasy games experimented with different combat systems. The other ATB system is also used in other Square games, most notably Chrono Trigger (1995). Final Fantasy XIII also uses the ATB system, with some variations. On March 16, 1992 Square Co., Ltd. filed a United States patent application for the ATB system under the title, "Video game apparatus, method and device for controlling same", and was awarded the patent on February 21, 1995.
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