Amazon.com12-inch singles of the '70s spell disco, pure and simple--they were invented to make it easier for DJs to keep a favorite groove going longer, and at their best, they shattered the three-minute constrictions of pop radio. This disc focuses on hardcore club-goers' favorites that took advantage of their six or seven minutes to build, plateau, break down, rebuild, and climax, or at least to sustain a colorful buzz. So alongside familiar pop-disco classics, it's got some swell obscurities by the likes of the Gibson Brothers, Good Times costar Ralph Carter, and Bionic Boogie. And in the middle of the swooping strings and clattering bongos, there's a surprise: Kraftwerk's "Trans Europa Express," with its foreshadowing of hip-hop and modern techno. --Douglas Wolk