Commercially released CD singles can vary in length from two songs (an A side and B side, in the tradition of 7-inch 45-rpm records) up to six songs like an EP. Some contain multiple mixes of one or more songs (known as remixes), in the tradition of 12-inch vinyl singles, and in some cases, they may also contain a music video for the single itself (this is an enhanced CD) as well as a collectible poster. Depending on the nation, there may be limits on the number of songs and total length for sales to count in singles charts.