We have radio to thank for inventing classic rock. Conceived as a programming format, it emerged in the ’80s when stations began devoting heavy airtime to a mix of beloved titans from the ’60s and ’70s (The Rolling Stones, Led Zeppelin, Bob Seger) and then-current hitmakers (Tom Petty, John Mellencamp) whose music contains heavy echoes of the vintage stuff. Even when classic rock opens its ranks to ’90s alt-rockers such as Soundgarden, it’s because they sound old-school. In terms of stylistic variety, the format boasts considerable leg room. Classic rock rotation can and does include soaring ballads from Pink Floyd, The Beatles and Elton John, and even the occasional glam nugget from David Bowie. Yet at the end of the day, the format definitely relies heaviest on thunderous hard-rock anthems perfect for Friday night parties or powering you through your workday.