With Windows 8, Microsoft tried - not entirely successfully - to make tablets part of a continuum that goes from number-crunching workstations and high-end gaming rigs through all-in-one touchscreen media systems and thin-and light notebooks down to slender touch tablets, all with the same OS, aiming for the best of both of today's computing worlds. What will it do for the next version of Windows?
Despite rumours of an aggressive development and shipping schedule, there's no official word about what's in the next version of Windows, but there are plenty of rumours (many of them from Chinese enthusiast sites that claim to have leaked builds), plus more reliable information from job adverts for the Windows and Windows Phone teams.
There are also patents, which may or may not be relevant, and some rare comments from developers on the Windows team. Here's what we've heard about Windows 9 and what we think is happening.
Windows more often: Windows 9 and Windows Blue
Job adverts for Windows and Windows Phone and LinkedIn profiles for developers on the Windows Server team all refer to "Windows Blue" in relation to a future version of Windows, Windows Server and Windows Phone.
That's only a codename and it's a codename not for the specific versions of these operating systems but for the new development cadence, where Microsoft puts out new releases of Windows, Windows RT and Windows Server every year, the way it already does for Windows Phone.
The next version of Windows is being referred to by Microsoft people who post their details on LinkedIn as Windows 9; as usual, that will be a codename that might change.
Screenshots claiming to show a leaked build show the kernel number as Windows 6.3; that just means that Microsoft is still being careful not to break applications that look for the Windows version number.
That's why Windows 7 was version 6.1 internally and Windows 8 is version 6.2; it doesn't mean this is 'only a service pack'. (What would normally have been Windows 8 SP1 was released through Windows Update before Windows 8 shipped in October 2012.)
Windows 9 release date
Microsoft communications chief Frank Shaw said Microsoft wasn't ready to talk about how often Windows might come out when we spoke to him in January, but he agreed "you have certainly seen across a variety of our products a cadence that looks like that; Windows Phone is a good for example of that, our services are a good example of that".
The rumours say Windows 9 will be finished in July or August 2013; that's a year after the RTM (release to manufacturing) of Windows 8. We don't know if it will be available to users straight away through Windows Update or if PC makers will get time to test and integrate updates for their systems (the RTM version could go on MSDN (Microsoft's Developer Network Platforms site) in July, giving hardware partners a month to test before release in August).
We also don't know if Windows 9 will be available as an upgrade from Windows 7 that you can buy as a standalone product or if you'll have to have Windows 8 to get the upgrade (which would explain new Windows business chief Tami Reller talking about "multiple selling seasons" for Windows 8, as well as rumours that Windows 9 will be either a free upgrade or part of an upgrade service you can subscribe to).
Microsoft seems to be on track; rumours say the first milestone, M1, was finished in mid February, putting the team halfway through the development cycle, with milestone 2, which may be released publicly as the Milestone Preview in a few months (perhaps May or June, to incorporate bug fixes in a July or August release).
Windows 9 features
To be competitive with iOS Windows RT has to get annual updates and it would make no sense not to release those updates to the WinRT runtime for Windows 8 as well, but the job ads say there's more to the next version of Windows than that with improvements to "the start screen; application lifecycle; windowing; and personalization… enhancing ease of use and the overall user experience".
Screenshots claimed to come from leaked builds show a new version of Internet Explorer, IE 11 (which isn't surprising - and might explain why IE 10 for Windows 7 has taken so long, if the IE team has been concentrating on this).
Other rumours say the Search charm will show results from multiple apps automatically, instead of waiting until you click another app in the list to see is search results. This would be more like the universal search in Windows 7 which showed results from Explorer, Outlook and other search providers in the same list of results.
Windows 9 to be cheaper, smaller, with more apps
In the last Microsoft earnings call CFO Peter Klein made it clear that Microsoft has got the message that Windows 8 tablets need to be cheaper; "we know that our growth depends on our ability to give customers the exciting hardware they want, at the price-points they demand."
One of the rumours about Windows Blue is that it will be optimized to run on 7" and 8" tablets - a form factor where Microsoft is losing out to Apple and Google right now.
That would explain rumours saying Windows 9 will improve "scaling"; if apps can be scaled down automatically, developers won't have to rewrite apps to run on different resolutions and screen sizes.
Another revealing Microsoft job advert talks about having Windows Phone and WinRT apps run on both Windows Phone and Windows. "Do you wish the code you write for Windows Store apps would just work on the Windows Phone and vice versa? If so, then this is the role for you! We are the team leading the charge to bring much of the WinRT API surface and the .NET Windows Store profile to the Phone."
That sounds like a longer term goal, given that the job advert was on the Microsoft Careers site at the beginning of February, and it's being driven by the Windows Phone team (we don't expect to see the next version of Windows Phone until the autumn), but it could give developers an incentive to write apps for the Windows Store and give Windows 9 users more to choose from. Scaling apps to fit different size screens would help here too.
Windows 9 power management
A recent Channel 9 video featuring Bruce Worthington, who leads the team working on Windows power management fundamentals, included some rather technical details about saving power in Windows and the improvement in Windows 8.
"If you look at the number of times we would wake up the CPU per second," he explained, "for Windows 7 you would typically see numbers on the order of one millisecond. We would literally be waking up the CPU a thousand times per second. If you look at Windows 8, on a clean system, we have numbers that are better than a hundred milliseconds. "
Now that Windows Phone 8 is based on the Windows Phone kernel, power management has to get better. "Now we're looking forward to the next release and we can get even farther - especially as we start interacting more and more with our phone brethren.
"They want us to be quiet for multiple seconds at a time. They even talk about minutes in some scenarios which is pretty far afield for us, to be thinking about minutes of being completely quiet. At least getting into the multi-second we're definitely ready to think about that."
Especially with Haswell bringing Connected Standby to Core systems, not just low-power Atom tablets, saving power looks like a priority for Windows 9 (especially if it comes out at the same time as Intel's new chips.
"For the next release there's all kinds of things we've already identified that are going be quite challenging but at the same time the user is going to get a tremendous boost forward," Worthington promised.
Windows 9 gestures and experiences
There are features we predicted for Windows 8 based on Microsoft patents and technologies we've seen demonstrated by Microsoft leaders like CTO Craig Mundie that didn't make it into the OS. There are features Microsoft plans for every version of Windows that get cut to ship on time; sometimes they reappear, sometimes they don't.
Kinect-based 3D gestures might be on the cards this time around, especially as we hear that some notebooks will soon get 3D cameras - although from other suppliers rather than Microsoft.
Using two cheap webcams rather than an expensive 3D camera could make gesture recognition hardware cheap enough for laptops and then you could wave at the screen from a distance.
And maybe Direct Experience will arrive in Windows 9. The patent explains this as a way of starting Windows to play media files in a special purpose operating system and there are improvements in Hyper-V for Windows Server 8 that Microsoft could use to make Windows 9 work better for this, like being able to move a virtual machine from one place to another while it's running.
Maybe that would even work with the next version of the Xbox - which will be based on the Windows kernel and is expected to ship in the autumn.
One obvious question is whether Windows 9 will be 64-bit only - something that Microsoft threatened even before Windows 7 shipped - but that's going to depend on what chips are in PCs.
ARM is 32-bit now and even when 64-bit ARM chips come along Microsoft may want compatibility with Windows 8 and 9 tablets. And although Intel is talking about 64-bit Atom systems, if Atom Windows 8 tablets have sold well, Windows 9 will need to support them.