Microsoft is finalising the feature set for Windows 9 and targeting an April 2015 release date for the OS, as it looks to move on from the disappointment of Windows 8.

Codenamed "Threshold", details about the Windows 9 are expected to be announced at the Build 2014 conference in April, Microsoft watcher Paul Thurrott suggested on Supersite for Windows.

Changes are expected to be made to the Metro/Modern UI, with a "windowed mode" for desktop expected to be one of the key inclusions.

Microsoft will not be showcasing a preview of Windows 9 at Build as development has yet to start. The conference is expected to focus on Windows Phone and the newly launched Xbox One console, sources told Thurrott.

Windows 8 has been struggling to gain traction in the market since its release in October 2012. Despite claiming to have sold 100 million licenses in May 2013, many Windows 8 PCs come with the option to downgrade to Windows 7. So the true number of PC running the new OS is thought to be much lower.

Many enterprise users are still migrating from the 10-year-old Windows XP operating system and have chosen to upgrade to Windows 7, which comes sans the Metro interface.