Not long ago, the phrase "Windows cloud" was an oxymoron; no two words could be further apart in meaning. But cloud computing is evolving quickly, and Windows clouds are finally taking shape.I'll get to Microsoft in a moment, but first an update on Amazon Web Services, which is well ahead of Microsoft in delivering Windows as a service. Last October, Amazon introduced Windows Server 2003 as an option on its Elastic Compute Cloud (EC2). Beginning at 12.5 cents per hour, AWS customers can run their Web sites, Web services, and applications on virtual Windows Server instances, with Microsoft's SQL Server Express, Internet Information Services, and ASP.net layered on as necessary. If you need more than that, the costs go up. At the high end, AWS charges $3.20 an hour for a Windows Server instance running on a more powerful CPU with authentication services and full SQL Server database.

Amazon this week expanded its Windows support by offering Windows Server instances in Europe and making it possible to launch and manage those instances from the AWS Management Console. On top of that, Amazon is offering an additional Windows Server "availability zone" in the United States, giving users another way to build resiliency into their hosted Windows apps.

Other Windows-as-a-service cloud vendors include GoGrid and Layered Technologies.

What about Microsoft? When it unveiled Windows Azure and Azure Platform Services at PDC last October, Microsoft didn't say when its cloud OS would ship. Speaking to financial analysts last week, Steve Ballmer indicated Azure would be ready by year's end. I say "indicated" because Ballmer hinted at a ship date, but didn't commit to one. He said Microsoft would have "the ability to go to market" with Azure by year's end.

Steven Martin, Microsoft's senior director of developer platform product management, cleared up the ambiguity this week in an interview with InformationWeek. Martin said "a commercial offering is slated for the end of this calendar year," adding that Azure services would be "competitively priced" and "consumptive in nature," a reference to pay-per-use pricing.

Windows in the cloud has been slow to develop, but we now know when Microsoft plans to deliver, and you can count the months on two hands. Now the discussion can begin to shift from when Windows clouds will happen to who wants them and why.