When Microsoft launched Windows 10 S - its stripped-down version of Windows - earlier this year, it assured people that anyone buying a device with the OS could upgrade to Windows 10 Pro for free until the end of 2017. Now, Microsoft has extended the offer by another three months.

The Chrome OS-style Windows 10 S launched in May 2017, primarily as an alternative to Google and Apple in the education market. As it only runs Windows Store apps, Microsoft said Windows 10 S offers better security and performance compared to the full-fat version of Windows, making it suitable for students and even businesses whose workers don't require full desktop functions.

It had been the case that anyone other than students who wanted to move to Windows 10 Pro from Windows 10 S after 2017 would have to pay $49 for the privilege. But the company has decided to extend the deadline, due to the fact the Windows Store still lacks some popular applications.

"For those that find they need an application that isn't yet available in the Store and must be installed from another source, we're extending the ability to switch from Windows 10 S to Windows 10 Pro for free until March 31, 2018. We hope this provides increased flexibility for those people searching for the perfect back-to-school or holiday gift," writes Raphael Aquino Jose, Senior Product Marketing Manager for Surface.

In the same blog post, Microsoft announced that Surface laptops are now available in different colors outside of the US.

While Microsoft places the reason for this extension firmly on the Windows Store's dearth of apps, it could be that Windows 10 S isn't proving as popular as Microsoft hoped. The fact that Bing-powered Edge is its default browser probably hasn't helped.