Worldwide shipments of personal computers (PC) slipped to 7.9 percent in the third quarter of the year according to industry observers, driven down by weak sales in the United States.

According to data released by market research firm, IDC, international shipments of PC's expanded at roughly 11 percent on a year-to-year basis, however, poor performance from dominant U.S. manufacturers brought aggregate sales down.

This quarter's results show a similar volatility to last quarter, with strong international sales and growth in portables reflecting continued demand while we saw weak results for Dell and the U.S. market overall, said Loren Loverde, director of IDC's Worldwide Quarterly PC Tracker.

Dell has had some negative publicity recently regarding its battery recall but it is hard to attribute the third quarter results to bad publicity alone. Dell will likely be very aggressive in the fourth quarter, and we will see how similar battery recalls affect other vendors. These factors may cut into fourth quarter growth, but overall we don't see a broad threat to fourth quarter growth.

Dell shipments fell nearly 7 percent year on year in the U.S. Hewlett-Packard was able to leverage strong growth in international markets and relatively strong performance in the United States to boost overall volume incrementally ahead of its rival, IDC said.

Both Dell and HP are currently tied for market share, holding 17.2 percent each, the firm said. The computer manufacturers are also both experiencing a shift in the types of machines being sold.

In the U.S. market, the focus continues to be on the transition from desktops to notebooks, with notebook growth being the sole bright spot while desktop shipments continued to decline, said Bob O'Donnell, vice president, Clients and Displays at IDC. The impact of Dell's decline was particularly acute in the U.S. and led to a shrinking of the market versus the same period last year.

The outlook for growth in the second half of the year has been under some scrutiny as replacement activity has declined and the delayed launch of Vista gets more attention.