LOS ANGELES — Ray Ozzie, Microsoft Corp.'s chief software architect, today detailed Windows Azure, a cloud computing version of its operating system that the software vendor says will enable developers to build and host online services on a Windows-based IT infrastructure.

Windows Azure is the foundation of a new Azure Services Platform that is designed to compete with Amazon.com Inc.'s Elastic Compute Cloud (EC2) service as a scalable application-hosting environment, Ozzie said during a keynote speech at Microsoft's Professional Developers Conference, which kicked off today in Los Angeles. Microsoft is releasing a Community Technology Preview version of the Azure Services Platform to PDC attendees and eventually will make the technology available worldwide through its data centers.

The announcement of Windows Azure was expected; Microsoft CEO Steve Ballmer had said during a public appearance in London on Oct. 1 that the company was readying a Windows cloud offering and would announce it within a month.

According to Ozzie, a team of Microsoft developers began working on Azure just before Amazon unveiled EC2 in beta mode two years ago. Just last week, Amazon removed the beta tag and said that EC2 is now ready for production uses, while also adding beta-level support for Windows and Microsoft's SQL Server database. Previously, EC2 only supported Linux.

Ozzie verbally tipped his hat to Amazon for bringing its cloud offering to market before Microsoft and other vendors. "All of us are going to be standing on their shoulders," he said, as the IT industry increasingly transitions from selling software that's installed on corporate networks to running applications over the Internet via cloud computing environments hosted by large vendors.

However, Ozzie added that Microsoft had "somewhat broader and different objectives" than Amazon in developing Azure. Unlike Amazon, he noted, Microsoft has the responsibility to support a vast global network of software developers as well as all of the applications that already have been built on top of Windows, SQL Server and its other infrastructure software.

Ozzie dipped into the past to show how cloud computing has evolved beyond the virtualization and utility models that he said have been present in corporate IT systems for 30 years or more. Previously, companies created networks for their own employees and didn't expect to be serving customers and business partners outside the firewall, he said. But, he added, "things are materially different when building systems to serve the world of the Web."