(This article is about albums of recorded music. For other uses, see Album (disambiguation).) Albums of recorded music were developed in the early 20th century, first as books of individual 78rpm records, then from 1948 as vinyl LP records played at  33 1⁄3 rpm. Vinyl LPs are still issued, though in the 21st century album sales have mostly focused on compact disc (CD) and MP3 formats. The audio cassette was a format used from the late 1970s through to the 1990s alongside vinyl.