For years, IBM's massive technology services arm has hogged the limelight, the symbol of its shift away from its old reliance on the "big iron" of mainframes and other hardware.

It is software, though, that has quietly taken up the running. With little fanfare, Big Blue's software arm, second only to Microsoft in size, has emerged to become the driving force behind the latest overhaul at IBM, capped in the final months of last year with growth of more than 10 per cent.