Microsoft has unveiled details of the Azure cloud computing platform at its Worldwide Partner Conference in New Orleans.

In November the first datacentres go live offering enterprises the Windows-based online hosted application platform.

Datacentres in the US, Dublin and Singapore will be open for businesses to deploy applications on what Microsoft is touting as an inexpensive, massively scaleable platform, with no hardware management for users.

In essence, the service offers a pay-as-you-go "virtual" Windows Server to host .Net-based business applications on the internet.

The service will be available via three subscription models with service-level guarantees for each of the three key elements of Azure - the Windows Azure compute function, SQL Azure database component, all glued together with Azure .Net services.

Microsoft UK developer and platform evangelism director Mark Taylor said one of the biggest challenges for enterprises, and one which some organisations could not previously overcome, would be allowing data out of their "safe havens ".

"Microsoft is offering the choice for firms of being able to work inside the cloud or behind your firewall," he said.

The roadmap set out by Microsoft sees November 2009 as the commercial launch date, offering three purchasing options for the service - pay as you go; a subscription-based model which gives discounts if firms make a specific commitment over time; and a volume licensing model comparable to that used for Microsoft's enterprise packages.

The pricing for Azure services is split into service price, charges for storage and then charges for data inbound or outbound from the application. A standard Windows Azure compute unit is $0.12 per hour, with storage charges of $0.15 per month, with 10,000 transactions costing $0.01.

SQL Azure comes in Web and Business Editions. The Web Edition uses a 1GB database for $9.99 per month, while the Business Edition uses a 10GB database for $99.99 per month.

For the .Net services package, service bus messages will cost $0.15 per 100,000, while inbound and outbound data from the application will be charged at $0.10 and $0.15 per GB respectively.

Azure services will also come with service- level agreements (SLAs) for each component. For instance, the compute function comes with an SLA that specifies if the uptime is less than 99.95 per cent in a month, customers will be given 10 per cent SLA credit. For storage availability, if the uptime is less than 99.9 per cent, again a 10 per cent SLA credit will be given. There will also be an " all services" SLA that gives a 25 per cent SLA credit if uptime is less than 99 per cent.

A Microsoft spokesman said there will also be tools for managing Azure cloud services.

"We'll provide something similar to our System Center Configuration Manager package, but targeted at metering and monitoring Azure. Currently we're working to create a cohesive and consistent interface, but we'll also expose the application programming interfaces [APIs], allowing you to use management tools from other vendors," he said.