The distinction between retro and modern is heavily debated, but it usually coincides with either the shift from 2D to 3D games (making the fourth the last retro generation, and the fifth the first modern), the turn of the millennium and the increase in online gaming (making the fifth the last retro generation, and the sixth the first modern), or the switch from analog to digital for audiovisual output and from 4:3 to 16:9 aspect ratio (making the sixth the last retro generation, and the seventh the first modern). They can be played on original hardware or in modern emulation.