Mainframe computers sound like dinosaurs of the technology world, but they are far from extinct. Their suitability for processing large volumes of transactions makes them a vital tool of online commerce and e-government. Given the money that has been sunk into applications that run on them, switching costs can be high.

This is a market that is almost totally dominated by a company with which it was once synonymous: IBM. Four decades after it was pressured into making concessions to rivals, Big Blue faces no serious mainframe competition. So it is appropriate that US anti-trust regulators, following in the tracks of their European counterparts earlier this year, have opened a new investigation.