Windows 8's user share surged last month, while Windows XP's plummeted by a record amount, a metrics company said this weekend.

October's statistics from Net Applications put the combined user share of Windows 8 and Windows 8.1 at 16.8% of the world's desktop and notebook systems, an increase of 4.5 percentage points from September. Last month's climb was the largest in the operating system's two-year history and almost equal to its best four-month increase.

Windows 8 accounted for 18.4% of the personal computers running Windows in October, a gain of 5 percentage points from the month before. The difference between the numbers for all personal computers and only those running Windows was due to the fact that Windows powered 91.5% of all personal computers in October, not 100%.

With its stunning growth, Windows 8 blew past the uptake tempo of Windows Vista, the OS that had set the failure benchmark. At the point in Vista's post-release timeline that corresponded to October, the 2007 edition ran on 15.7% of all personal computers and on 16.8% of all Windows PCs. The latter is the most credible comparison, because it accounts for the slightly greater dominance of Windows at the time. (When Vista was in its 24th month after launch, Windows powered 93.7% of all personal computers.)

The increase in Windows 8's user share -- a rough measurement of the number of personal computers running a specific operating system -- came in the first full month after a strong back-to-school sale season wrapped up.

Net Applications data is not authoritative -- the company measures operating system use by tallying browser visitors, then aggressively modifies the numbers to account for countries where it has sparse information -- but if the numbers hold up in future months, October would represent a turning point for the perception-plagued Windows 8.