Windows marketing manager Erwin Visser says in a blog post that customers can now start testing the operating system in their environments. Windows 8.1 Enterprise Preview builds on the Window 8.1 Preview which is currently available, adding premium features designed to address mobility, security, management and virtualization needs of today’s enterprise.

The Register notes that among the major changes, the new release allows IT departments to control the layout of the Start screen – and, optionally, to prevent users from changing the layout themselves – to enforce consistency across workgroups.

Access to apps and files can also be restricted for users or groups, to prevent employees from running unauthorized software on company equipment. Admins can even lock down a device so that it can only run a single Windows Store app in a kiosk-like mode.

Also new in the Enterprise Preview, IT departments can now more easily side-load custom Windows apps onto domain-joined devices. Other versions of Windows 8.1 and earlier versions of Windows 8 have required admins to jump through several hoops to load apps from sources other than the Windows Store, including installing a special product key onto each machine.

Windows 8.1 Enterprise also includes a Windows To Go Creator, which lets admins build a customized Windows 8.1 desktop that can be booted from an external USB drive.

There is one catch, though. Unlike the earlier Windows 8.1 Preview, the Enterprise Preview is available only as a full install image, rather than as a Windows Store download for existing Windows 8 devices, and is meant to be installed on test machines only.

Customers have around four and a half months to test the Enterprise Preview, as it will expire on January 14, 2014.