It had to do with depth of the groove, the spindle speed, and the recording time. 78-RPM Records The playing time of a phonograph record depended on the turntable speed and the groove spacing. At the beginning of the 20th century, the early discs played for 2 minutes, the same as early cylinder records. The 12 inch disc, introduced by Victor in 1903, increased the playing time to three and a half minutes. Because a 10-inch 78-rpm record could hold about three minutes of sound per side and the 10-inch size was the standard size for popular music, almost all popular recordings were limited to around three minutes in length. Microgroove Vinyl In 1948, the 12-inch Long Play (LP) 33 1/3 rpm microgroove record album was introduced by the Columbia Record Company at a dramatic New York press conference on June 21, 1948. In February 1949, RCA Victor released the first 45 rpm single, 7 inches in diameter, with a large center hole to accommodate an automatic play mechanism on the changer, so a stack of singles would drop down one record at a time automatically after each play. Early 45 rpm records were made from either vinyl or polystyrene. They had a playing time of 8 minutes. A far lengthier and more detailed history of the Vinyl Record can be found here - http://en.wikipedia.org/wiki/Gramophone_record