Windows 8 OS
Microsoft released the Windows 8 OS to PC manufacturers on August 1. Developers can download the OS starting August 15 via their MSDN subscription. Windowsteamblog

Microsoft released the final version of Windows 8 to MSDN and TechNet subscribers August 15. While the developers can download it from MSDN subscription, the IT professionals testing Windows 8 can access the final version through TechNet subscriptions.

There is a 90-day trial version for the general consumers.

The trial version made available in several languages in 32-bit (x86) and 64-bit (x64) editions provide an opportunity to test the operating system ahead of its debut October 26.

The Verge has reported that Windows 8 Enterprise edition includes features of Windows 8 Pro and more business-focused options including Windows To Go, a new way to run Windows 8 installation from a USB key.

For those wanting to test the OS prior to its availability in stores, the trial version offers a safe bet. However, the operating system has to be reinstalled once Windows 8 and Windows 8 Pro are made available October 26, the Verge added.