The demand for these machines increased, & different manufacturers responded by creating their own models with distinctive features and designs that helped to further the development of slot machines. Slot machine design & operation evolved alrummy gold 2ong with technology during the 20th century. With the advent of electromechanical machines in the 1960s, features like multiple paylines and bonus rounds were made possible, along with more intricate gameplay. But more complex gaming options did not start to compete with classic slots until the 1970s with the introduction of video slots. Classic slots continued to be popular because of their nostalgic value and simple gameplay, even with the shift in attention towards video slots.