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Classic hits is a radio format which generally includes rock and pop music from 1964 to 1989. The term is sometimes erroneously used as a synonym for the adult hits format (which uses a slightly newer library stretching from the 1970s through the 1990s), but is more accurately characterized as a contemporary style of the oldies format. Most stations focus on pop hits of the late 1960s through the early 1980s.
The term "classic hits" is believed to have its birth at WZLX Boston when the station converted from "adult contemporary" to a format composed of the hipper tracks from the oldies format and album tracks from popular classic rock albums. The goal was to attract and magnetize two groups of baby boomers: those who didn't want the doo-wop and pop they found on the oldies stations, and those who didn't like the more heavy metal side of AOR stations.
Over time, the "classic hits" format has evolved into more of a station's slug line than of a tightly focused music library shared by the stations who use the term. The first branching-off in the late '80s led to stations becoming more "classic rock"-based, and the second reincarnation manifested itself in the premises of the "Jack FM" and the "Arrow" formats. Some of the 21st-century versions are based on a music library mostly consisting of classic rock-style hits from the 1970s, along with R&B and pop hits from the late 1960s through the mid-1980s. In many of the cases, the stations are merely oldies stations that evolved into a more up-tempo sound with more newer songs, and the term is now considered a more appealing name than "oldies" to listeners and advertisers alike.
Variations of the core playlist vary greatly and include playlists composed of only pop-leaning classic rock. Others, while indeed leaning rock, also feature some soul, and Motown music as well. Most "classic hits" stations are heavy on music from the 1970s, with a moderate amount of music from the 1960s, and a decent amount of hits from the 1980s.
Until the past few years, most classic hits stations have either leaned towards pop hits of the 60s through the 80s or were actually classic rock stations without a lot of hard rock. Classic hits stations typically do not play pre-1964 music, except for a few especially popular or enduring songs such as early Beach Boys hits, or more generally 1960 to 1963 songs. In most cases, more pop-leaning classic hits stations evolved quietly and gradually from being traditional oldies outlets.
As with most formats, and perhaps even more so, the classic hits format can be programmed tightly to include only a few hundred well-tested songs in heavy rotation (common with major, commercial stations) or can take a much broader approach encompassing music beyond the narrowest definitions of the format. An extreme example of the latter is Seneca Nation owned WGWE, which is centered on the traditional classic hits era music but plays music spanning from the big band era to the present.
Notable classic hits stations include WROR-FM in Boston, Massachusetts; WCBS-FM in New York City; WOGL in Philadelphia; KLUV in Dallas, Texas; WKLH in Milwaukee; WOCL (105.9 Sunny FM) in Orlando, Florida, KOMA in Oklahoma City and WMJI (Majic 105.7) in Cleveland, Ohio.
In Canada 
The format has begun to make its appearance on a growing number of Canadian radio stations. One Canadian broadcasting company, Newcap Broadcasting, has adopted this format on a number of its stations. Two examples, such as CFXL-FM in Calgary and CKRA-FM in Edmonton, first began airing the new classic hits format.
There are other classic hits stations in Canada, such as CJOT-FM 99.7 in Ottawa, a French language one on CFOM-FM 102.9 in Quebec City, CING-FM 95.3 in Hamilton, Hamilton's web radio station Classic Hits Online and many others.