ZDNet

It's official: Microsoft has sent out invitations to a Sept. 30 event in San Francisco, where the company is expected to show off an enterprise technology preview of its next version of Windows, codenamed Threshold.

"Join us to hear what's next for Windows and the enterprise," the invitations say.

The invitations don't specify whether Microsoft will distribute the Windows Threshold tech preview bits at the event. But previous leaks have indicated Microsoft has been targeting late September or early October to make a first public preview of Threshold available.

Microsoft also is expected to release a first public preview of the Threshold version of Windows Server at the same time, sources have said.

The enterprise tech preview won't include all of the features that Microsoft is planning to deliver by spring, which is the rumored release date of Windows Threshold. Instead, sources have said, the enterprise tech preview will be focused on showcasing some of the changes Microsoft will be making to the "Desktop" with Threshold on Intel-based PCs.

Another preview -- one that will run on ARM-based Windows Phones and ARM-based tablet devices -- is expected in January or February, sources said.

Threshold, which may or may not ultimately be christened "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, sources have said.

By the time it's released, Threshold is expected to include a number of new features and interface changes designed to make the operating system work better with mice and keyboards.

Among the expected features in Threshold, according to sources, are a new mini-Start menu; the removal of the Charms bar; the ability for windowed Metro-Style apps to run on the Desktop; virtual desktops; and possibly inclusion of the Cortana personal digital-assistant technology.

Like Windows 8.1 Update (1), Threshold is expected to look and work differently on different types of hardware, based on hardware profiles. Microsoft officials are considering whether to make Threshold free to existing Windows 7 and Windows 8 users, sources have said, as an incentive to get them to upgrade.

This story originally appeared as "Microsoft invites media to meet the next version of Windows" on ZDNet.