Microsoft is obviously set to to detail its next major version of Windows - codenamed Threshold - in a press event scheduled for later this month. The company's "Windows event" in San Francisco is set for September 30th. The software maker is expected to deliver a "Windows Technical Preview" as well a first public preview of the Threshold version of Windows Server.

Threshold or possibly "Windows 9", is expected to be the last major operating system update for Windows. After Threshold, Microsoft is aiming to release smaller updates on a regular schedule, according to reports.

Screenshots and videos of the Windows Technical Preview have leaked over the web past week, revealing the addition of a new mini-Start, a virtual desktops feature, the removal of the Charms bar, the ability for windowed Metro-Style apps to run on the Desktop, and a Notification Center. Microsoft also appears to be tweaking its desktop user interface to improve the traditional icons, alongside some taskbar changes for future Cortana integration and virtual desktops.

The new operating system is expcted to be released next year. It is not clear whether Threshold will be free to existing Windows 7 and Windows 8 users.