In 1965, Barrett and Waters meet an experimental percussionist and an extraordinarily gifted keyboards-player — Nick Mason and Rick Wright respectively. The result is Pink Floyd, which more than 40 years later has moved from massive to almost mythic standing.

Through several changes of personnel, through several musical phases, the band has earned a place on the ultimate roll call of rock, along with the Beatles, the Stones and Led Zeppelin. Their album sales have topped 250 million. In 2005, at Live 8 — the biggest global music event in history — the reunion of the four-man line-up that recorded most of the Floyd canon stole the show. And yet, true to their beginnings, there has always been an enigma at their heart.

Roger 'Syd' Barrett, for example. This cool and charismatic son of a university don was the original creative force behind the band (which he named after the Delta bluesmen Pink Anderson and Floyd Council). His vision was perfect for the times, and vice versa. He would lead the band to its first precarious fame, and damage himself irreparably along the way. And though the Floyd's Barrett era only lasted three years, it always informed what they became.

These were the summers of love, when LSD was less an hallucinogenic interval than a lifestyle choice for some young people, who found their culture in science fiction, the pastoral tradition, and a certain strain of the Victorian imagination. Drawing on such themes, the elfin Barrett wrote and sang on most of the early Floyd's material, which made use of new techniques, such as tape-loops, feedback and echo delay.

Live, the Floyd played sonic freak-outs — half-hidden by new-fangled light-shows and projections — with Barrett's spacey lead guitar swooping over Waters' trance-like bass, while Wright and Mason created soundscapes above and beneath. On record they were tighter, if still 'psychedelic'. Either way, they sounded 'trippy'. And perhaps that was Barrett's intention. He certainly ingested plenty of LSD and other drugs, which didn't help his delicate mental balance.

Over the spring of 1966, the young band were regulars at the Spontaneous Underground 'happenings' on Sundays at the legendary Marquee Club, where they were spotted by their future managers Peter Jenner and Andrew King. And by the autumn, the Floyd had become the house band of the so-called London Free School in west London.

A semi-residency at the All Saint's Hall led to bigger bookings — at the UFO and the International Times' launch in the Roundhouse — as well as the recording of the instrumental 'Interstellar Overdrive' with the UFO's co-founder, producer Joe Boyd. (This track was later used on hip documentaries of the scene.) A signing to EMI followed in early 1967.

"We want to be pop stars," said Syd. In March, Boyd recorded Barrett's oddly commercial 'Arnold Layne' as a three-minute single. And with a Top Twenty hit to promote, the band took on a gruelling schedule of gigs and recordings.

They appeared at the coolest event of the summer, The 14-Hour Technicolor Dream in Alexandra Palace. They gave a concert under the banner 'Games for May' in a classical venue — the Queen Elizabeth Hall — where they displayed their theatrical ambitions through the use of props, pre-recorded tapes and the world's first quadraphonic sound system. (They received a lifetime ban for throwing daffodils into the audience.) And in June the Floyd released a single originally written for this event.

'See Emily Play', which was produced by EMI's Norman Smith, charted at Number Six and made it on to primetime TV's Top of the Pops three times (with Barrett acting increasingly strangely). This was followed in August by Pink Floyd's first LP, The Piper At The Gates of Dawn, which they recorded at Abbey Road next door to the Beatles, then working on Sergeant Pepper. Again making the Top Ten, the album is mainly Barrett's and is a precious relic of its time, a wonderful mix of the whimsical and weird.

Talking of which, Barrett's behaviour and output were threatening to bring the band down with him: refusing to speak, playing one de-tuned string all night, writing material like 'Scream Thy Last Scream, Old Woman with a Basket'. The band wanted to keep their frontman and hoped he would recover himself, so they asked David Gilmour — now back in London after a sojourn abroad — to take over Syd's role on stage, and thought Barrett might become their off-stage songwriter. They tried a few gigs as a five-piece. But in the end, they decided they could do without Barrett, and by March 1968 were in their second incarnation and under new management.


Set the Controls

Barrett went his way with Jenner and King, and later recorded two haunting solo albums — on which Waters, Wright and especially Gilmour helped — before retreating to Cambridge for the rest of his life. The other four acquired a new manager — Steve O'Rourke — and in a state of some consternation finished their second album, A Saucerful of Secrets (begun the previous year).

Lyrical duties had now fallen to the bassist Roger Waters. And apart from 'Jugband Blues' — a disturbing track by Barrett, who contributed little else — the album's standout moments included the title track and Waters' 'Set the Controls for the Heart of the Sun'.

This hypnotic epic signposted the style the band would expand on in the Seventies, its vision at first more appreciated by an 'intellectual' and European audience. The Floyd played the first free concert in Hyde Park, and laid down the soundtrack for the bizarre Paul Jones movie vehicle, The Committee. They toured continually, developing new material on stage as well as in the studio.

And they worked on the experience, in April 1969 revealing an early form of surround-sound at the Royal Festival Hall — their rebuilt 'Azimuth Co-Ordinator'. (The prototype, first constructed and used in 1967, had been stolen.) They worked on their concepts, too - at that concert, performing two long pieces fusing old and new material, entitled 'The Man' and 'The Journey'.

So their star continued its inevitable ascent. In July, the Floyd released More, less a soundtrack than an accompaniment to Barbet Schroder's eponymous film about a group of hippies on the drug trail in Ibiza. The same month, they played live 'atmospherics' to the BBC's live coverage of the first moon landing. In November, they released the double-album Ummagumma, a mixture of live and studio tracks — and that same month reworked its outstanding number, the eerie 'Careful With That Axe, Eugene', for Antonioni's cult film Zabriskie Point.

With Ummagumma at Number Five in the UK charts, and a growing reputation in both Europe and the US underground, the Floyd played some of the key festivals of their time — Bath, Antibes, Rotterdam, Montreux — and between October 1970 and November 1971, put out two more albums.

Atom Heart Mother, their first Number One, featured the Floyd in their pomp — 'I like a bit of pomp,' says Gilmour (who also made his first lyrical contribution with the gentle 'Fat Old Sun'). And Meddle included two timeless and largely instrumental tracks that showcased their lead guitarist in all his vertiginous, keening glory: 'Echoes', which took up the whole of Side One and began with a single 'ping' created almost accidentally by Wright, and 'One of These Days'.

Increasingly successful, in 1972 the band was still pushing the boundaries. They shot the film 'Live at Pompei' in a Roman amphitheatre, recorded another movie soundtrack for Schroder — Obscured by Clouds — and performed with the Ballet de Marseille. But more importantly, they began to work on an idea that would become their most popular album and with 45 million sold, the world's third biggest.

Provisionally entitled 'Eclipse' and honed through an extensive world tour, The Dark Side of the Moon was released in March 1973, and defies a potted critique here. Demonstrating Waters' talents as both lyricist and conceptualist, it was also a musical tour de force by Gilmour. But Waters was becoming de facto leader of the band — which in public at least was becoming less about the individuals than the experience.

That was (as Barrett had always intended) increasingly visual. The intriguing sleeve artwork commissioned from the ex-Cambridge outfit Hipgnosis was complemented by stage shows featuring crashing aeroplanes, circular projection screens and flaming gongs. There were backing singers on-stage and a guest slot for another pal from Cambridge, the saxophonist Dick Parry. In the dawning age of stadium rock, the Floyd were truly its masters.

Or maybe its servants? Even before Dark Side broke Middle America through FM radio — with the single 'Money' — alienation, isolation and mental fragility had long been Waters' themes. As a stadium performer, and a cog in the music business machine, he was becoming more prone to all three. As Barrett's ex-colleague, he had seen them embodied in his old friend. The results were evident in two of his best lyrics — for 'Shine On, You Crazy Diamond' and 'Wish You Were Here'. These tracks were the high points of the Floyd's next LP, also called Wish You Were Here, which was begun in January 1975 and released that summer.

Famously, Barrett briefly appeared unannounced at Abbey Road during the recording of 'Shine On' and shocked the band by his appearance and demeanour. It was the last time any of them saw him — but they were seeing less of each other, too. Personal and