Windows 8's uptake was even more sluggish when compared to Windows 7, the 2009 operating system that has flourished as much as Vista flopped.
By the end of its second month of availability, Windows 7 accounted for 6.2% of all Windows machines, or nearly four times that of Windows 8 as of Dec. 22.
At this point, it looks virtually impossible for Windows 8 to do as well as its immediate predecessor, at least in the short run: At the end of Windows 7's third month -- analogous to Jan. 31, 2013 for Windows 8 -- it had gained another two percentage points to end with an 8.2% share of all Windows systems.
In fact, Windows 7 continued to gain share in December, according to preliminary numbers from Net Applications. Through Dec. 22, Windows 7's usage share of all personal computers was 45.6%, or nine-tenths of a percentage point higher than at the end of November.
To put that in perspective, Windows 7 gained more than twice the share through Dec. 22 than did Windows 8.
Windows 8's failure to stay abreast of Windows 7 or even Vista is not hard to explain, said analysts, who have been predicting a weak reception for the new operating system, blaming a weak economy, the OS's confusing dual user interfaces, enterprise upgrade fatigue after migrating to Windows 7, and competition from rivals' tablets -- including Apple's iPad, Amazon's Kindle and Google's Nexus -- for customers' technology dollars.
Neither Vista nor Windows 7, of course, had to face competition from tablets.
And that, experts have said, is paramount. Because Windows' success is directly tied to the number of new PCs sold, sluggish system sales caused by defections to tablets translates into a slow-down in operating system's uptake.
And people, whether consumers or enterprise workers, are increasingly turning to tablets -- virtually all of which run a non-Microsoft OS -- as their preferred mobile device, reducing sales growth of Windows notebooks and generally stretching everyone's PC refresh cycle. Research firm IDC, for instance, recently raised its 2012 tablet sales forecast to 122 million devices, up 72% from 2011.
Earlier this year, IDC said that total worldwide PC shipments would reach 367 million in 2012, less than 1% above 2011's 364 million.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at 
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