Windows 10 is catching up to Windows 8.1, report says.

Windows 10 adoption hasn't caught up with Windows 8.1 yet, but it may be getting close. According to   AdDuplex , the split betwee...

Windows 10 adoption hasn't caught up with Windows 8.1 yet, but it may be getting close.

According to AdDuplex, the split between Windows 8.1 and Windows 10 devices is currently 61 percent for the former, and 39 percent for the latter.

If you don't count Windows RT devices such as Microsoft's Surface tablets, the ratio is 58.8 percent for Windows 8.1 to 41.2 percent for Windows 10. The data comes from 173 Windows Store that use AdDuplex for cross-promotional ads.

Granted, this is hardly a complete measure of Windows 10 usage, as AdDuplex isn't even counting devices that run Windows 8.0 or earlier. As we know from other metrics firms, Windows 7 is still the dominant version of Microsoft's operating system, running on roughly half of all laptops, desktops, and tablets.

In last month's market share data from NetMarketShare and StatCounter, Windows 10 was still far from overtaking even Windows 8.1. NetMarketShare showed a 69-31 split between the older and newer operating systems, while StatCounter found a 73-27 split.

In terms of user numbers, Microsoft itself has said Windows 10 was installed on 75 million machines  after four weeks. Thanks to the free upgrades Microsoft is offering to consumers running Windows 7 or higher, adoption has been faster than for any previous version of Windows.

Why this matters: AdDuplex's data is useful in showing how quickly devices with the Windows Store are moving to Windows 10. As the balance tilts away from Windows 8.1, developers could have more incentive to update their apps with full Windows 10 support, or even create Universal Apps that can run across phones, tablets, laptop and desktop PCs, and game consoles.