Day 273~366

Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min) is a measure of the frequency of rotation, specifically the number of rotations around a fixed axis in one minute. It is used as a measure of rotational speed of a mechanical component. In the French language, tr/mn (tours par minute) is the common abbreviation. The German language uses the abbreviation U/min or u/min (Umdrehungen pro Minute).
A gramophone record (phonograph record in American English) or vinyl record, commonly known as a record, is an analogue sound storage medium in the form of a flat polyvinyl chloride(previously shellac) disc with an inscribed, modulated spiral groove. The groove usually starts near the periphery and ends near the center of the disc. Phonograph records are generally described by their diameter in inches (12″, 10″, 7″), the rotational speed in rpm at which they are played (16 2⁄3, 33 1⁄3, 45, 78), and their time capacity, determined by their diameter and speed (LP [long playing], 12-inch disc, 33 1⁄3 rpm; SP [single], 10-inch disc, 78 rpm, or 7-inch disc, 45 rpm; EP [extended play], 12-inch disc, 33 1⁄3 or 45 rpm); their reproductive quality, or level of fidelity(high-fidelity, orthophonic, full-range, etc.); and the number of audio channels (mono, stereo,quad, etc.).

The long playing (nicknamed the LP; in full a 33 1⁄3 rpm microgroove) record is a vinyl record format, an analog sound storage medium. Introduced by Columbia in 1948, it was soon adopted as a new standard by the entire record industry. Apart from relatively minor refinements and the important later addition of stereophonic sound, it has remained the standard format for vinyl albums. 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 vinyl and played with a smaller-tipped “microgroove” stylus at a speed of 33 1⁄3 rpm. Each side of a 12-inch LP could play for more than 20 minutes. Only the microgroove standard was new, as both vinyl and the 33 1⁄3 rpm speed had been used for special purposes for many years, as well as in one unsuccessful earlier attempt to introduce a long-playing record for home use by RCA Victor.
Although the LP was suited to classical music because of its extended continuous playing time, it also allowed a collection of ten or more pop music recordings to be put on a single disc. Previously, such collections, as well as longer classical music broken up into several parts, had been sold as sets of 78 rpm records in a specially imprinted “record album” consisting of individual record sleeves bound together in book form. The use of the word “album” persisted for the one-disc LP equivalent.

The phonograph disc record was the primary medium used for music reproduction until late in the 20th century, replacing the phonograph cylinder record—with which it had co-existed from the late 1880s through to the 1920s—by the late 1920s. Records retained the largest market share even when new formats such as compact cassette were mass-marketed. By the late 1980s, digital media, in the form of the compact disc, had gained a larger market share, and the vinyl record left the mainstream in 1991. From the 1990s to the 2010s, records continued to be manufactured and sold on a much smaller scale, and were especially used by disc jockeys (DJ)s, released by artists in some genres, and listened to by a niche market of audiophiles. The phonograph record has made a niche resurgence in the early 21st century – 9.2 million records were sold in the U.S. in 2014, a 260% increase since 2009. Likewise, in the UK sales have increased five-fold from 2009 to 2014.



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