Investors tend to forget that some of the world largest PC companies are based in China, lead by Lenovo and Acer. The two companies run behind Dell (NASDAQ:DELL) and Hewlett-Packard (NYSE:HPQ) in global market share. But, that may be changing in a way that the two US companies will find unpleasant.

Research firm Gartner looked at PC sales around the world during the third quarter. According to Reuters, "Overall, worldwide PC shipments rose 15 percent from last year to 80.6 million units." To no one's surprise, growth in the US was slower, up 4.6%.

HP's global market share was 18.4% and Dell's was 13.6%. Acer rose to 12.5% making it the most improved of the three compared with last year.

Acer's secret is that it is selling netbooks, small PCs which usually cost under $500. Analysts have questioned whether consumers would want these because smartphones have many of the same functions. Acer has taken the gamble of ramping up production, a potentially risky move if the customers were not out there. The decision is giving them a chance to steal a march on the larger rivals.

The Acer move may say as much about what is wrong with US PC companies as its says about what is right at Acer. There are many people, especially in emerging markets, who are not likely to be able to spend $1,000 on a computer. And, the mobility of the US PC user is improving with the success of WiFi and 3G.

Dell and HP should be concerned every time they see someone walking down the street with a netbook. It has probably been sold to them by a competitor.

Douglas A McIntyre is an editor at 247wallst.com.