The LP (from long playing[2] or long play) is an analog sound storage medium, specifically a phonograph record format characterized by: a speed of 33+1⁄3 rpm; a 12- or 10-inch (30- or 25-cm) diameter; use of the "microgroove" groove specification; and a vinyl (a copolymer of vinyl chloride acetate) composition disk.

[4] LP was originally a trademark of Columbia[5] and competed against the smaller 7-inch sized "45" or "single" format by RCA Victor, eventually ending up on top.

[7][8] At the time the LP was introduced, nearly all phonograph records for home use were made of an abrasive (and therefore noisy) shellac compound, employed a much larger groove, and played at approximately 78 revolutions per minute (rpm), limiting the playing time of a 12-inch diameter record to less than five minutes per side.

The new product was a 12- or 10-inch (30 or 25 cm) fine-grooved disc made of PVC ("vinyl") and played with a smaller-tipped "microgroove" stylus at a speed of 33+1⁄3 rpm.

The King Biscuit Flower Hour is a late example, as are Westwood One's The Beatle Years and Doctor Demento programs, which were sent to stations on LP at least through 1992.

[16][17][18] Compton Pakensham, reviewing the event in The New York Times, wrote, "What we were not prepared for was the quality of reproduction ... incomparably fuller.

"[17] CBS Laboratories head research scientist Peter Goldmark led Columbia's team to develop a phonograph record that would hold at least 20 minutes per side.

According to the 1949 Columbia catalog, issued September 1948, the first twelve-inch LP was Mendelssohn's Concerto in E Minor by Nathan Milstein on the violin with the New York Philharmonic, conducted by Bruno Walter (ML 4001).

Three ten-inch series were released: 'popular', starting with the reissue of The Voice of Frank Sinatra (CL 6001); 'classical', numbering from Beethoven's 8th symphony (ML 2001), and 'juvenile', commencing with Nursery Songs by Gene Kelly (JL 8001).

The LP was not seriously challenged as the primary medium for listening to recorded music at home until the 1970s, however, when the audio quality of the cassette was greatly improved by better tape formulations and noise-reduction systems.

It offered a recording that was, theoretically, almost noiseless and not audibly degraded by repeated playing or slight scuffs and scratches.

[32] With the advent of sound film or "talkies", the need for greater storage space made 33+1⁄3 rpm records more appealing.

It was not until "microgroove" was developed by Columbia Records in 1948 that Long Players (LPs) reached their maximum playtime, which has continued to modern times.

Recording company executives believed upscale classical music fans would be eager to hear a Beethoven symphony or a Mozart concerto without having to flip over multiple, four-minute-per-side 78s, and that pop music fans, who were used to listening to one song at a time, would find the shorter time of the 10-inch LP sufficient.