Computing is undergoing one of its great periodic shifts. In its early days, most computing took place on mainframes. Ever-falling costs led computing to shatter-first into minicomputers, then into personal computers (PCs) and more recently, hand-held devices. Now communications is catching up with hardware and software and, thanks to cheap broadband and wireless access, the industry is witnessing a pull back to the middle. This is leading much computing to migrate back into huge data centres. Networks of these computing plants form ‘computing clouds’ - vast, amorphous, delocalized nebulae of processing power and storage.