Worldwide PC processor shipments dropped sharply in the fourth quarter of 2008, according to the latest figures from IDC, and apparently the downward spiral will continue through the first half of 2009. Specifically, the market research firm claims preliminary numbers suggest CPU shipments will decline by about 15 percent in 2009 compared with last year.

In the fourth quarter of 2008, processor unit shipments declined 17 percent quarter over quarter and 11.4 percent year over year, while market revenue declined 18 percent over the previous quarter and 22.2 percent compared to the year-earlier period to $6.78 billion. Moreover, IDC points out that without Intel’s Atom things would have been much worse, with an estimated unit shipments drop of 21.7 percent in Q4.

Intel should probably also thank the Atom for a 1.1 percent market share boost in the fourth quarter to 81.3 percent, which came mostly at AMD's expense who suffered a 0.9 percent drop in the same timeframe to grab 17.7 percent of the market while VIA took a tiny 0.4 percent. You can check some additional figures here.