Riff-rockers Led Zeppelin have become one of only three acts to have four or more Diamond albums, according to the Recording Industry Association of America. Diamond status signifies more than 10 million copies shipped. The Beatles have five Diamond albums and country singer Garth Brooks has four. Physical Graffiti (1975) is the latest Zeppelin album to be certified Diamond, following Led Zeppelin II (1969), Led Zeppelin IV (1971) and Houses of the Holy (1973). The band recently released its first greatest-hits set, Early Days: The Best of Led Zeppelin Vol. 1.