When mechanical slot machines were initially introduced in the late 19th century, that is when the history of 777 slots began. Some of the most recognizable symbols in the history of slot machines are thesata king . cherries, bars, and lucky sevens that adorned the three reels of these early machines. Due to its long-standing associations with luck & good fortune, the number 7 quickly gained popularity as a symbol in slot machines, inspiring the development of 777 slots. Electronic and eventually digital slot games were created as a result of the design and operation of slot machines evolving along with technology.