Windows 8 and Windows 8.1 now power more personal computers than the still-strong, senior-citizen Windows XP, according to the latest statistics from analytics vendor Net Applications.

The growth of Windows 8 and 8.1, and the not-quite-corresponding decline of XP, should make it easier for Microsoft to make its public goal of putting Windows 10 on a billion devices by the end of July 2018.

For the first time in Net Applications' tracking, the combined user share of Windows 8 and 8.1 was larger than that of XP: In May, the Windows 8 duo accounted for 18% of all Windows personal computers and 2-in-1s, while XP powered 16%.

User share is a rough estimate of the percentage of the world's online users who ran a specific OS during a given month, and is tracked by Net Applications using visitor tallies to its customers' websites.

Windows XP launched in 2001, and was officially retired from support more than a year ago. In operating system terms, it's Methuselah: When it debuted, Apple was more than five years away from announcing the iPhone and Google was almost that far from becoming a verb.

Since April 2014, when Microsoft put XP out to pasture, its user share has fallen by almost half.

Meanwhile, Windows 8 + Windows 8.1 booked its highest-ever user share last month, with the latter -- a free upgrade to the former since the fall of 2013 -- now representing 78% of the total.

All those data points must be encouraging to the management at Redmond, Wash.-based Microsoft as it starts to wrap up Windows 10, which will release as a free upgrade on July 29.

Microsoft has gone aggressive on Windows 10, making the unprecedented move to give away upgrades to consumers and small businesses running Windows 7 or Windows 8.1. The firm is so confident of that push that it recently committed to putting the OS on a billion devices within 24 to 36 months.

That job will be easier with more machines running Windows 8/8.1, as upgrades are adopted by a larger percentage of those running the immediate predecessor than those running older code, who have stuck with creaky software because they cannot afford a new device, face compatibility problems if they migrate, or simply find two or more generations' worth of changes unpalatable.

By reducing XP's prevalence -- almost certainly through new device purchases at this point -- the number of systems unable to handle Windows 10 will also fall.

Windows 7, which represented 63% of all Windows PCs, took a dip in May, part of the growth story for Windows 8.1 that month. But because the 2009 Windows 7 is eligible for the free upgrade to Windows 10 -- and because those users are much more likely to migrate to the new OS than they were to the bifurcated Windows 8/8.1 -- that number won't be a concern to Microsoft.

The company has talked repeatedly of wanting to move as many of its current customers to Windows 10 as possible, and do that sooner rather than later. With the user base flush with devices running Windows 7 and 8/8.1 -- 81.5% of the total, also a record -- that goal looks more attainable than ever.