Arcades are the most common and preferred genre of video games. Starting with the arcade machines which were activated by inserting a coin, the history of the genre backtracks to 1978's Space Invaders. Due to the limited time of gameplay, arcades often have short levels and structured as platformers with simple mechanics including jumping, shooting or moving around the screen space. There are little-to-none puzzles in such video games, and a lot of in-game situations are incredibly skill-dependent which is also very much reminiscent of arcade machines past — the leaderboard was an essential element awaking the competitive and exciting element in players. The primary feature to early arcades is their unbeatable nature — most of them focus the attention on an infinite amount of levels making the title practically unbeatable. The most significant examples of the arcades are Pac-Man, Donkey Kong Jr., and Mario Bros.