Enterprises can now run Windows Server in Amazon's cloud for up to 750 hours per month at no charge, using the AWS (Amazon Web Services) Free Usage Tier, the company announced.

With this announcement, enterprises that run applications on Windows Server can try Amazon's cloud at no cost, the company said. Users can select from a range of pre-configured Amazon Machine Images with Microsoft Windows Server 2008 R2.

The Windows Server images run on a micro-instance, or virtual server, which includes 613 MB of memory and support for 32-bit or 64-bit software.

The Free Usage Tier was launched in 2010, but has so far only been available with Linux. Enterprises can now run both operating systems for up to 750 hours per month for one year. Beyond that, enterprises can pay regular fees, which start at $0.02 per hour for Linux and $0.03 per hour for Windows.

If usage exceeds the limitations of the tier users also have to open their wallets. For example, if two Windows Server 2008 R2 instances are active for 400 hours each during a single month, the user has accumulated 800 hours of usage, of which 750 hours will be free, and the remaining 50 hours will be billed at the standard price.

The tier also includes limited use of Amazon's load balancer, storage services (S3 and Elastic Block Store) and the SimpleDB database.