For a couple of years now we've considered monthly desktop operating system market share from StatCounter and Netmarketshare. Of late we've added data from the US government's analytics service, on grounds that US the traffic to US government web sites it measures - all 1.53 billion visits in the last 90 days - is as good a collection of public data as any other we've been able to find.

In January Uncle Same found Windows 8.1 slumping from December's 15.57 per cent of visits to US sites to a new low of 11.95 per cent. Windows 10 leapt from December's 12.85 per cent to 17.89 per cent.