Beginning in the mid-1970s, they began contracting with what would become over 100 stations by the 1980s. Abrams' SuperStars format, previously developed at WQDR, was based on extensive research, focused on the most popular artists such as Fleetwood Mac and the Eagles, and also included older material from those artists. While his format was not quite as constricted as Top 40 radio, it was considerably more restricted than freeform or progressive radio. Their firm advised program directors for a substantial segment of AOR stations all over the U.S. By the late 1970s, AOR radio stations discarded the wide range of genres embraced earlier on to focus on a more narrowly defined rock sound. The occasional folk, jazz, and blues selections became rarer, and most Black artists were effectively eliminated from airplay. Whereas earlier soul, funk, and R&B artists like Stevie Wonder, War, Sly Stone, and others had been championed by the format, AOR was no longer representing these styles and took a stance against disco. In 1979, Steve Dahl of WLUP in Chicago destroyed disco records on his radio show, culminating in the notorious Disco Demolition Night at Comiskey Park. What links the freeform, progressive, and AOR formats is the continuity of rock artists and songs carried through each phase. Programmers and DJs of the freeform and progressive phases continued to cultivate a repertoire of rock music and style of delivery that became the foundations of AOR and classic rock radio. Those AOR stations, which decided to stay demographically rooted, became classic rock stations by eschewing newer bands and styles for which their older listeners might have tuned out. Those that did not fully evolve into classic rock stations generally attempted to keep their older listeners through careful dayparting – playing large amounts of classic rock during the workday, while newer material was played at night when the listener base skewed younger. Programming Most radio formats are based on a select, tight rotation of hit singles. The best example is Top 40, though other formats, like country, smooth jazz, and urban all utilize the same basic principles, with the most popular songs repeating every two to six hours, depending on their rank in the rotation. Generally, there is a strict order or list to be followed, and the DJ does not make decisions about what selections are played. AOR, while still based on the rotation concept, focused on the album