Microsoft's free upgrade offer is over - and it's clearly had a big impact. But Microsoft still has a lot of work to do.

Image: Nick Heath / TechRepublic

Microsoft's year-long offer of a free upgrade to Windows 10 has now finished, albeit with a couple of loopholes still to be closed.

Since the deal was launched last year there are now more than 350 million devices running the new operating system, mostly thanks to the offer.

It's not especially surprising that users have quicker to upgrade to Windows 10 than earlier versions: Microsoft was giving it away for free, after all.

Microsoft's offer was, to an extent, bowing to the inevitable: since the rise of the smartphone with regular free mobile OS upgrades, consumers increasingly expect to get new desktop OS upgrades for free (indeed, Mac users have done since 2013).

The touch-centric look-and-feel that arrived with Windows 8, which confused and upset many users, was onther reason for the Windows 10 offer. Giving Windows 10 away for free helped Microsoft put that painful negative reception behind it, and in the process got rid of much of the Windows 8 installed base still out there (has any version of Windows appeared and disappeared so quickly?).

Image: TechRepublic, date from Microsoft

It's not just the UI that's different: Windows 10 is part of Microsoft's shift in line with the world of apps, subscriptions and the cloud. To make that big ecosystem shift work, Microsoft needs as big an audience as possible on Windows 10 in order to attract developers to build for Windows as well as iOS and Android.

So what was the impact of the offer, in detail? It's worth remembering that the free upgrade offer was quite tightly drawn: it was only available for consumers with PCs running Windows 7 and Windows 8.1 (and Windows Phone 8.1).

Data from NetMarketShare suggests that the giveaway has certainly had an impact, with a clear decline in Windows 7 and 8 as Windows 10 has climbed.

In July last year Windows 7 accounted for 61 percent of PCs accessing the web, while Windows 8 had 13 percent.

According to the Netmarketshare data, by July this year Windows 7 stood at 47 percent and Windows 8.1 at a mere eight percent, while Windows 10 has grabbed a 21 percent share. Left out in the cold, and excluded from the offer, Windows XP has only dropped from 12 percent to 10 percent.

That would suggest that the offer has created a significant critical mass for Windows 10 among consumers who would otherwise have been reasonably happy to stick with Windows 7. And as noted above, it has also taken a big chunk out of Windows 8.

In the short term, the free Windows 10 offer has done what it needed to do in terms of putting Microsoft's new OS on a good footing. Perhaps more importantly, the momentum of the upgrades so far -- mainly by consumers -- will place more pressure on businesses to start their upgrades. Companies will be more comfortable kicking off their own Windows 10 upgrades knowing that most of the bugs will have been cleaned out. They will also know that many of their own staff will be familiar with the new UI through having used it at home.

However, it's not all plain sailing: Microsoft originally aimed for one billion Windows 10 devices within three years, but recently admitted that it wouldn't get there -- largely because Windows smartphone sales have been plunging for some time as the company has cut back that part of the organization.

That's going to matter more and more in the long term: the PC is important, but the future belongs to mobile, so Microsoft needs to come up with a strategy for mobile that works, and fast.

Microsoft Weekly Newsletter Be your company's Microsoft insider by reading these Windows and Office tips, tricks, and cheat sheets. Delivered Mondays and Wednesdays Sign up today

More on Windows 10

Windows 10 one year on: Has it been a success for Microsoft?

Windows 10, Android, iOS, and the billion user question (ZDNet)

Those free Windows 10 upgrades are over. Now what? (ZDNet)

Microsoft is updating Windows 10 again, in its latest bid to win you back (CNET)