Windows runs on 330 million PCs worldwide. Three hundred PC manufacturers around the world install Windows on their machines; thousands of devices plug into Windows computers; and tens of thousands of third-party software applications run on Windows. And a crucial reason Microsoft holds more than 90% of the PC operating system market is that the company strains to ensure software and hardware that ran on previous versions of Windows will also work on the new one—compatibility, in computing terms.

As a result, each new version of Windows carries the baggage of its past. As Windows has grown, the technical challenge has become increasingly daunting. Several thousand engineers have laboured to build and test Windows Vista, a sprawling, complex software more than 40% larger than Windows XP.

“Windows is now so big and onerous because of the size of its code base, the size of its ecosystem and its insistence on compatibility with the legacy hardware and software, that it just slows everything down,” observed David B Yoffie, a professor at the Harvard Business School. But last Thursday, Microsoft reorganised the management of its Windows division. Steven Sinofsky, 40, a senior VP, was placed in charge of product planning and engineering for Windows and Windows Live, a new web service that lets consumers manage their e-mail accounts, instant messaging, blogs, photos and podcasts in one site. The move is seen as an effort to bring greater discipline to the Windows group. “But this doesn’t seem to do anything to address the core Windows problem; Windows is too big and too complex,” said Michael A Cusumano, a professor at the Sloan School of Management at the Massachusetts Institute of Technology.