The simple mechanism of these early machines allowed players to spin the reels by pulling a lever, & payouts were based on the arrangement of the symbols. The desilive slotsgn and operation of slot machines evolved along with technology, and in the 1960s & 1970s, electronic machines that enabled more intricate gameplay were introduced. The world of slots games underwent a radical change as a result of the digital revolution, especially with the introduction of online casinos in the late 1990s.