<p>I recently posted a question about Azure... <a href="https://stackoverflow.com/questions/315879/is-azure-an-operating-system-or-a-framework">is it really an OS?</a>  I understand the technical details, and I got a lot of fuzzy answers... I really want to know... what do you think is the difference between an OS and a Framework?</p>

<p>Just for reference, Azure will be built on top of Hyper-V servers and the virtual machines will be running vanilla Windows Server 2008.  It will run services that creates a cloud on top of the many virtual machines which is called Azure.  Windows is calling Azure an OS.  </p>

<p>I am trying to understand how to define the difference between an OS and a framework.</p>

An OS is the thing that directly interfaces with the machine, be it virtual or real. It has to expose syscalls that handle input devices, output devices, sound, networking, and all the other things that we take for granted these days. It also often provides some kind of UI which uses these services to make it easy to use/useful for an end-user. It needs to have device drivers to work with video cards, sound cards, etc. (Once again, these can be virtualized).
A framework is... something built on top of the OS. It, too, exposes an API, but they are often not so low-level as the one the OS exposes.