If you are wondering why Microsoft is now suddenly launching TV commercials that claim Chromebooks are not real notebooks, the latest U.S. sales figures for PC and tablet sales from the NPD Group research firm may be a big clue. According to their newest report, Chromebooks claimed 21 percent of all commercial channel-based notebook sales and eight percent of all commercial PC and tablet sales in the US between January to November 2013.

The report adds that in the first 11 months of the year, 1.76 million Chromebooks and Android-based tablets were sold, compared to just 400,000 units in 2012. By contrast, Windows notebooks showed no sales growth in the past year, according to NPD, although sales of Windows desktops did rise up by 10 percent in 2013.

The spike in Chromebooks sales is good news for Google, along with its third party OEM partners like HP, Dell, Samsung, Acer and others who have all released notebooks based on Chrome OS in the past year. The news isn't as good for Microsoft, which now sees Chromebooks as a real threat to its Windows OS-based laptop sales.

Overall, 14.4 million desktops, notebooks, and tablets were sold through U.S. commercial sources in the first 11 months of 2013. That's up 25.4 percent compared to 2012, which only showed a 3.1 percent increase.

Source: NPD Group | Image via Google