It may come as a shock to those who have grown up with the company and still think of themselves as young. But on Saturday Microsoft will celebrate its 40th birthday. As it enters middle age, Microsoft is still the world’s biggest software firm, with annual revenues of $87 billion and profits of $22 billion. But it is much less important than it once was: it responded flat-footedly to the shift of computing from desktop PCs and corporate servers to smartphones and vast data centres (alias the “cloud”). To make Microsoft relevant again, Satya Nadella, its boss of 14 months, is doing all he can to end its dependence on Windows, the dominant operating system of the desktop years—and to turn it into a company that “builds stuff that people like”. If he can do that, Microsoft may yet be thriving at 50.