MS is calling Azure an Operating System.
To me, it feels much more like a framework. I am having a bit of trouble defining the two separately. I have a general intuition, but I am not articulate enough to really say if Azure is really an OS or just a framework sitting on top of Operating Systems.
I've just been listening to the Deep Fried Bytes Podcast #20 wherein, they interview Steve Marx, the Windows Azure Program Manager, and he explains it all.
From what I can gather thus far (haven't finished all the podcast) it works like this:
Microsoft have a ton servers running Hyper-V which can run virtualized instances of windows server 2008
You can start/stop/reboot an arbitrary number of these virtual win2k8 servers using an API, and you get charged only based on what you use.
The platform which controls this start/stop/reboot/crash recovery/provisioning/billing/etc is Windows Azure. They jokingly refer to it as the 'windows server overlord'
You define roles for these VM's, which can be either
You can use the windows azure API's to start/stop them - eg: "Give me 5 instances of my web role and 3 instances of my worker role"
Data gets stored by their storage services, and can be
These VM's have a bunch of other services available to them - Live Services for windows live stuff, .NET services, SQL Services if you need a full-blown SQL server for relational data, Sharepoint services if you want sharepoint, etc.
All this stuff rolled up together is the Windows Azure Services Platform
My take - Giant Marketing fail. Confusion abounds. MS seem to always do this kind of 'roll it all up into a single buzzword' thing though (.NET 5 years ago, anyone?). I really wish they would stop it
http://stackoverflow.com/questions/240455/what-is-windows-azure seems to answer this, perhaps?
Quoting @daok:
The Azure™ Services Platform (Azure) is an internet-scale cloud services platform hosted in Microsoft data centers, which provides an operating system and a set of developer services that can be used individually or together. Azure’s flexible and interoperable platform can be used to build new applications to run from the cloud or enhance existing applications with cloud-based capabilities. Its open architecture gives developers the choice to build web applications, applications running on connected devices, PCs, servers, or hybrid solutions offering the best of online and on-premises.
Azure reduces the need for up-front technology purchases, and it enables developers to quickly and easily create applications running in the cloud by using their existing skills with the Microsoft Visual Studio development environment and the Microsoft .NET Framework. In addition to managed code languages supported by .NET, Azure will support more programming languages and development environments in the near future. Azure simplifies maintaining and operating applications by providing on-demand compute and storage to host, scale, and manage web and connected applications. Infrastructure management is automated with a platform that is designed for high availability and dynamic scaling to match usage needs with the option of a pay-as-you-go pricing model. Azure provides an open, standards-based and interoperable environment with support for multiple internet protocols, including HTTP, REST, SOAP, and XML.
Key components of the Azure Services Platform include the following:
Technically, Azure is a set of services running on vanilla Windows 2008 Servers running virtually inside of Hyper-V. Your app runs on those services, abstracted away from the actual operating system. Because of this, they are calling Azure a "Cloud Operating System". Unfortunately, these answers don't answer my question... so...
I re-formatted my question to something more generic: What is the difference between an OS and a Framework?
Another way I have heard Windows Azure pitched is "infrastructure as a service". Meaning that you don't have to think about the operating system in the same way as if using a server or VM that you tweak.