The next version of Windows, which will start arriving tomorrow, won't do a couple of the things that you'd normally expect a new operating system to do as standard.
It won't immediately make Microsoft a lot of money from licences because it's going to be a free download for the majority of consumers. And it won't provide a much-needed shot in the arm for PC sales either, because many existing PCs will be able to run it, sparing consumers the need to buy a new machine to use the new OS. Windows 10 is the clearest illustration yet of how much the business model around Windows has changed in just a few years.
What Windows 10 will do, however, is fix many of the perceived problems that made Windows 8 so hard to sell: even now, three years after launch, it only has scraped together a 13 percent share of the PC market; Windows 7 (51 percent) and Windows XP (24 percent) still outrank it, according to NetMarketShare.
With Windows 8, Microsoft was generally considered to have put too much emphasis on making the OS look good on a tablet and not enough on making it work well on a PC, which is where it would mostly be used. This upset and confused Microsoft's loyal customer base; Windows 10 walks that back, at least a bit.
Microsoft's ambitions still reach beyond the PC, however. It eventually wants one billion devices to be running Windows 10 - including smartphones and tablets, as well as PCs. From that point of view, Windows 10 is not about selling Windows licenses or PCs, but something far bigger and broader.
The problem with that ambition is that there are already operating systems for smartphones and tablets which are doing a sterling job, namely Android and iOS, and it's not clear that there's enough in Windows 10 to unseat either of them.
"Microsoft will face a long road ahead to gain Windows share in mobile," said Forrester analyst Frank Gillett in research on the new OS. "While it will win a growing share of enterprise tablet purchases, the plans for Windows 10 don't show enough potential to create a differentiated mobile experience that will draw developers and customers away from iOS and Android."
That's an issue because, while the PC market isn't going anywhere soon, it isn't growing fast either: much of the growth in hardware around the world is likely to come in the form of tablets (perhaps hybrid PCs) and smartphones - and maybe even wearables. Windows 10 does address all of those form factors, but Microsoft doesn't have as much momentum in those areas as its rivals.
Still, Windows 10 is likely to strengthen Microsoft's position in the PC world - a free upgrade means that most consumers will take the plunge, followed eventually by businesses. That standardization of so many customers onto one version of Windows should make it easier for application developers to reach more customers more quickly.
And because it should be much easier to make Windows 10 apps run on tablets and smartphones as well as PCs, that consolidation might just create - over time - that critical mass of apps that Microsoft needs to reignite its mobile ecosystem. Equally, its rivals have an enormous head start that it is hard to see Microsoft overturning any time soon.
By getting it right where Windows 8 went wrong, with Windows 10 Microsoft may well win the battle it lost in the past - but it remains to be seen if it can win the war it must fight in the future.
Windows 1.0 to 10: The changing face of Microsoft's landmark OS
More on Windows 10