Microsoft is set to announce a new operating system in April, a U.S. tech blogger reports, seen as vital for the embattled tech company.

Microsoft is set to introduce its newest OS, currently code named Threshold and likely to be Windows 9, at its annual Build conference in April, with a full release date set for April 2015, tech watcher Paul Thurott wrote on his winsupersite.com blog.

Windows 8 has not been selling in the numbers for which Microsoft hoped. The latest release, Windows 8.1, is currently in use on less than 25 million PCs.

Arriving just as tablet computers with their touch-screen paradigm took off, Windows 8 tried to please both traditional PC owners and tablet owners, but its touch-centric Metro interface pleased almost no one.

Windows 9 will probably attempt to take a step backward, Thurott wrote.

"This is the release my sources previously pegged as being the one that will see the return of the Start menu and the ability to run Metro-style apps on the desktop alongside desktop applications,: he wrote.

"Threshold needs to strike a better balance between meeting the needs of over a billion traditional PC users while enticing users to adopt this new Windows on new types of personal computing devices," he wrote. "In short, it needs to be everything that Windows 8 is not."