With Windows 8 and now Windows 8.1, 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. Could it be that we'll get Windows 8.2 first?
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.
Cut to the chase
What is it? A complete update of Windows
When is it out? We expect it to be out in 2015
What will it cost? We really have no idea. But if Windows 8 is anything to go by, it won't cost much to upgrade
Windows Blue turned out to be Windows 8.1 rather than a completely new version of the Windows OS, which is what we'd expect Windows 9 to be.
There's certainly a 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.
While still just a codename, Windows 9 has also been referenced by Microsoft in a job posting, spotted by MSFT Kitchen on 13 March 2013.
The ad, for a Bing Software Development Engineer, says that the team will be delivering products "in areas including Windows 9, IE11 services integration, touch friendly devices including iPad and more."

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".
We 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. But it may not be with us for a while yet - Windows business chief Tami Reller has talked about "multiple selling seasons" for Windows 8, meaning that we'll likely have several versions of it.
Windows 9

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."
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.
Cut to the chase
What is it? A minor upgrade for Android, to follow on from Android 4.3 Jelly Bean
When is it out? The rumors say October 14 or October 31
What will it cost? Nothing, it'll be a free upgrade
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.
Windows 9
Direct Experience would start up a media version of Windows if you booted with a USB stick of music files plugged in
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.