It's easy to forget that Pink Floyd were around long before The Dark Side of the Moon made them one of the biggest bands in the world. That 1973 album and classic No. 1 LPs like Wish You Were Here and The Wall that followed often shadow the fact that before Dark Side, the band recorded seven albums, none of which managed to crack the Top 40.

The massive box set The Early Years -- 1965-1972 is a sturdy reminder that Pink Floyd had a long history before The Dark Side of the Moon logged more than 900 weeks on the chart. Over the course of 27 CDs, Blu-rays and DVDs, the group's history -- starting with demos recorded by the group the year it formed and ending with a remixed version of the album that came out right before the one that finally broke them -- unfolds piece by piece, as members come and go (singer and guitarist David Gilmour replaced the band's original visionary, Syd Barrett, not long after its debut album was released) and the group wipes away the psychedelic shadings of its early work and expands into more experimental territory.

The Early Years divides the story into six volumes (plus a bonus seventh one that collects some stray tracks and videos somehow left off the other discs), most devoted to individual years that neatly divide into album eras. And with each successive record, Pink Floyd inched closer to the thick, progressive sound that anchors Dark Side. The musical space between 1967's debut album, The Piper at the Gates of Dawn, and 1972's Obscured by Clouds, the LP released nine months before Dark Side, is immense. But The Early Years  -- which documents it all step by step with previously unreleased songs, live cuts, concert footage, TV and radio appearances and more -- makes it all seem like the most logical of progressions.

How did Pink Floyd get from their odd debut single, "Arnold Layne," about a clothes-stealing transvestite, to the epic "Echoes," one of their most celebrated pre-Dark Side tracks? Songs like the 25-minute live version of "Atom Heart Mother" with brass, choir and strings from a 1970 BBC session and the various soundtrack work collected here connect the dots.

Because none of the seven albums from the period are represented here, at least not with versions of songs you've heard before, The Early Years tends to get a bit repetitive at times (hope you like "Set the Controls for the Heart of the Sun"; that A Saucerful of Secrets track is here a lot). To their credit, though, Pink Floyd were constantly evolving their material onstage. For example, a live version of "Interstellar Overdrive" with Frank Zappa barely contains the familiar riff that drives the song.

And those moments, along with the handful of previously unreleased songs from Barrett's short tenure with the group, are the set's most intriguing ones. Videos documenting various promotional appearances through the years -- where the band was forced to lip- synch songs, with Gilmour often filling in for the departed Barrett -- also help to form a more vivid picture of the first couple years, when they were often faced with condescending and occasionally rude TV hosts.

The Early Years isn't designed for casual fans, the ones Roger Waters later railed against on albums like The Wall. It's a deeply committed collection with more than 125 tracks and 15 hours of video that aim to be the definitive word, outside of the albums, on the band's first chapter. There were bigger, and grander, things to come. But without these songs, they never would have gotten to the masterpieces that made them one of rock music's biggest bands.

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