HTML5 is going to bring us some powerful and sophisticated web apps, says Steven Sinosfsky, President of Microsoft's Windows and Windows Live Division.

But if you're expecting the head of the Windows division to be worried about that, he suggests you think about how browsers will achieve their ambitions.

"The world for a while went down this path [with] the browser as this tiny little program you just ran on top of the OS, this cool thing that didn't care about the device hardware or the OS. That can work for a period of time but underneath the hardware is changing rapidly and eventually the hardware capabilities transcend that.

The browser needs an OS to utilise the GPU

"This idea that what you're running a browser on doesn't matter is very hard to maintain when the hardware is getting so capable. All browsers say they want to do location awareness now; that's hardware dependant. To do rotation you have to know that the thing got rotated. Browsers need to know what's going on on the hardware to move forward."

And HTML5 makes that worse, not better. "In the set of specs that will make up HTML 5 there are things that are going to have to take advantage of a whole new generation of hardware to be implemented.The whole way you have to architect and write a browser has to change to architect these things."

Take the DirectText font rendering in IE9 that uses the new vertical sub-pixel positioning in Windows Vista and 7 or the GPU acceleration he announced for IE9 last year, that other browser vendors quickly said they'd implement. It needs Windows (or another OS that lets apps use graphics acceleration) to work.

"The browser can't just use the GPU; you need a whole OS to understand the GPU. You have to understand which OS facilities are going to go and use it to take advantage of the GPU. If you want to be just-in-time capable you can't just say 'I want to use a core'; you have to ask the OS what core you can use.

"SVG (Scalable Vector Graphics) is just the first example of this. When you think about what are these amazing programs people are going to write down the road, to take advantage of this whole new big opportunity of HTML5 you have to take advantage of the OS. We think using the APIs in Windows is a good thing - and we think writing a browser that uses them is the only way to really do a great job on HTML5."

He dismisses the idea that this gives Microsoft an advantage over other browser companies; "No browser vendor needs us to tell them what to do. If you want to use SVG, you're going to need to use the GPU.

He does joke for a moment that the programming interfaces IE uses are "all secret!" but then immediately points out that it's just DirectX – the same system hundreds of apps and games already use.