The remaining members of Pink Floyd (David Gilmour, Nick Mason, Roger Waters & Richard Wright) convened and began sharing song ideas for their 8th studio album in late 1971 and early 1972 at Decca Record's West Hampstead Studios in Broadhurst Gardens, London - and then at a warehouse owned by The Stones at 47 Bermondsey Street, South London.
In this pre-Internet age, they were able to test-drive their material before its release without fear that it would end up on YouTube - so Floyd knocked the album into shape over several months of road work. The first full-length performance was at the Guildhall in Portsmouth, England, on January 21st, 1972, after which almost the entire year was spent with the band performing it live, interspersed with visits to Abbey Road studios from May onwards to work on tracking/finishing individual songs.
Released on May 1, 1973, the 43-minute long "Dark Side of The Moon" went on to sell 50 millions albums worldwide and remained on the Top 100 chart until this date in 1988 - a remarkable 741 weeks!
Roger Waters said in 2003 that "Dark Side" was "An expression of political, philosophical, humanitarian empathy that was desperate to get out." He said it was about "all the pressures and difficulties and questions that crop up in one's life and create anxiety, and the potential you have to solve them or choose the path that you?re going to walk.". . .which explains why it's required listening for most college freshmen.