Today Microsoft will show off the newest version of its Windows operating system. A lot rides on Windows 10, even if the system is no longer the software company’s be-all and end-all. Its predecessor, Windows 8 (Microsoft has skipped 9), flopped with both consumers and companies. Microsoft promises to do better this time: the new incarnation has the “start” button that was omitted at first from Windows 8, to users’ consternation; an updated web-browser, codenamed Spartan, is expected too. Refreshing PCs still matters to Microsoft, but is no longer enough. In mobile devices its market share remains minuscule; buying Nokia’s handset division has made little difference. Microsoft says Windows 10 will bring it closer to a common system for devices of all sizes. But people seem happy with Windows on their PCs and Apple’s iOS or Google’s Android on their phones. Indeed, you could argue that the new Windows is already here: it’s called Android.