By the time U2 finishes its 360° world tour in Pittsburgh next July, it's expected it will have generated about $1 billion in revenue.

That makes U2 one of the only bankable businesses left in Ireland (even if it now does its banking in Holland for tax reasons), and allows it to invest in the spectacle that draws people out to the stadiums.

It was the spectacle, or rather the technology behind the spectacle, that drew me to Mt Smart last week.

Dell wanted to show me how its workstations get used to process the video which gives those back in the stands something to look at.

Going over the lip of the bowl and I'm struck by the Claw, the 50-metre high, four-legged steel rig which holds the speakers and cylindrical video screen over the circular stage.

In the twilight Jay-Z was haranguing the crowd, his sound punched out by the Clair sound system, which is billed as the largest speaker assemblage in touring history.

The tour is U2's first in a 12-year deal with the promoter Live Nation, so expect them back before 2020.

Jay-Z's hits done, a swarm of black-clad elves cover the stage quickly hustling away kit and dismantling platforms to reveal U2's waiting amps - despite the millions of dollars in digital kit hidden away underneath the stage, the core of the sound is going to be the wood and wires of The Edge's smorgasbord of classic guitars processed at the first instance through Vox amps.

The sun drops over the horizon, Bowie's Space Oddity comes over the PA, the lights come up, the band comes on, all cocky strut and big gesture, the crowd goes into its roar.

Bono immediately sets off on a tour of the ramps which are connected to the main stage by two moving bridges.

Wireless connections mean bands are no longer tethered to their amplifiers, and Bono makes the most of it to preserve the illusion of intimacy among such a big crowd.

Cameras run on rails along the edge, sucking in images to be projected high above on the LED screen.

On previous tours U2 cancelled shows because of weather damage to video screens.

The 500,000 LED pixels in the transforming screen are weather resistant, and they're made up into elongated hexagonal segments mounted in a way that allows them to spread apart with a scissor-like motion during parts of the concert.

As well as live footage from the 14 cameras, the crew back in the tower mix in footage from previous concerts, news images, colour effects, and, after the performance of One Tree Hill, a roll call of the 29 miners killed at Pike River.

The tour's architect, Mark Fisher, told CNET News that while in general the technology behind U2 360° isn't new, the way it's being used is, from the large number of computers and electric motors that control the motion of the screen and the moving lights to the computers that map the video picture on to the transforming screen.

"All of this automation and programming is possible because the computers available in 2009 (when the tour started) are more powerful and cheaper than they were when we created the Vertigo tour in 2005," Fisher said.

After the Vertigo tour U2 ended its relationship with Apple Computer, opening up opportunities for other vendors.

Dell's contribution includes off-the-shelf, rack-mounted Precision workstations that allow the crew to work with raw footage back in their hotel room, rather than be tied to the control room, as was the case with the earlier generation of custom-built systems.

While the high tech images are going off above, all around me people are using their phones to record stills or video grabs whenever Bono or The Edge or Adam Clayton or even Larry Mullen come out on to the ramps.

Such technology means the days of camera and recorder bans are well over.

Bono uses the ubiquity of cameras to provide light during the encore of Ultraviolet (Light My Way) - a step up from the cigarette lighter spectaculars of yore, but probably still making a contribution to the concert's massive carbon footprint.

In total, the tour is expected to generate as much carbon as flying a passenger plane to Mars - for which the band has bought offsets.