Microsoft has released a free version of Windows 8, which you can use for 90 days - but there are a couple of catches you should be aware of before taking the plunge.

Aimed at developers, but open to all, the Windows 8 Evaluation for Developers gives users a full, unrestricted copy of the Release To Manufacturing (RTM) version of Windows 8, free to use for a 90 day period. Designed for use by those who can't afford a subscription to the Microsoft Developer Network (MSDN) or other software licensing schemes, it allows administrators to test out their systems and software for compatibility before the general release of the operating system in October.

Before you rush to download it, be aware of caveat number one: the version of Windows 8 on offer is the Enterprise Edition, which is designed for corporate use. In other words, expect to see more of a focus on using the software with Active Directory domains and Exchange servers, rather than getting the most out of your games with DirectX 11.1.

Secondly, once your 90 days are up there's no upgrade route to a final release: the software will simply stop working, and you'll have to create a fresh installation of a new operating system. You'll be able to back up your files, of course, but system settings won't be transferable to final release versions of Windows 8 - even for those who are getting hold of the official Enterprise Edition at launch.

Still, free is free, and unlike previous Windows 8 previews this represents the final and finished state of the operating system - at least, the version which will be available for corporate mass-licensing. If you'd like to check it out for yourself, you can download the demo directly from Microsoft.