Singles have been issued in various formats, including 7-inch, 10-inch and 12-inch vinyl discs. The most common form of the vinyl single is the 45 or 7-inch, the names are derived from its play speed, 45 rpm and the standard diameter 7-inch.
The 7-inch 45 rpm record was introduced in 1949 by RCA as a smaller, more durable and higher-fidelity replacement for the 78 rpm shellac discs. The first 45 rpm records were monaural, with recordings on both sides of the disc. As stereo recordings became popular in the 1960s, almost all 45 rpm records were produced in stereo by the early 1970s.
Although 7 inches remained the standard size for vinyl singles, 12-inch singles were introduced for use by DJs in discos in the 1970s. The longer playing time of these singles allowed the inclusion of extended dance mixes of tracks. In addition, the larger surface area of the 12-inch discs allowed for wider grooves (larger amplitude) and greater separation between grooves, the latter of which results in less cross-talk. Consequently, they “wore” better, and were less susceptible to scratches. The 12-inch single is still considered a standard format for dance music, though its popularity has declined in recent years.
Depending on its type, in addition to the song itself, a single may include remixes of the song, additional songs, a music video for promoting the single, and a collectible poster.