Windows XP's market share has tumbled to just 17.2 percent — a fall of 6.7 percentage points — according to Netmarketshare's latest figures, published on Saturday by Net Applications.
At the same time, the combined market share of Windows 8 and Windows 8.1 has climbed to 16.8 percent, which is only 0.4 percentage points behind the venerable XP.
Perhaps next month's results will show that XP hasn't really fallen so far so fast, and the October numbers are a statistical blip. It's certainly very unusual to see an operating system's market share fall by 6.7 percentage points. In fact, previously, it took XP almost a year to fall by this amount.
However, it's also possible that last month's figures — which showed XP unexpectedly holding its own (down from 23.89 percent to 23.87 percent) — were wrong. Perhaps XP actually dropped a couple of percentage points last month, and another couple of points this month. This would make sense in the context of users migrating away from XP, now that it's no longer supported.
XP's dramatic decline has come with a dramatic increase in Windows 8.1's market share, from 6.7 to 10.9 percent. Again, a one-month increase of 4.25 percentage points is very unusual and possibly unique. If we believe Netmarketshare's previous numbers, it only grew by 0.32 percentage points (from 6.38 to 6.67 percent) between May and September.
Given the known sales of PCs to consumers this summer, I didn't believe those numbers were correct. In other words, Netmarketshare's "sudden leap" may include another historical correction.
If Netmarketshare has finally got it right this month, then it requires a significant change in perception. The story so far this year has been that XP has been in steady decline but it still accounted for roughly a quarter of the PC user base (including Macs and Linux machines), while Windows 8 and 8.1 stumbled along in the low teens.
Now, suddenly, the Windows 8 and 8.1 combo has closed the gap and is about to overtake XP.
If Netmarketshare has actually got it wrong this month, then this will become apparent later. Either way, since Microsoft doesn't publish accurate numbers for its installed base, these are the best numbers we've got.
Finally, Windows 7 remains the clear market leader with 53.05 percent of the market. There's also the "other" category of operating systems that didn't make the graph. These include Windows Vista (2.82 percent), Windows NT (1.64 percent), Linux (1.41 percent), and Mac OS X 10.10 (1.18 percent). All the numbers are based on tracking visits to websites.
It's somewhat hard to believe that Vista still has twice as many users as Linux, but the Vista users don't spend their time shouting about it.