Strong laptop sales are marking a rapid shift in PC buying habits.

In the third quarter, worldwide laptop shipments grew 37%, a rate that even edged out several major quarters in 2003 and 2005, when growth hit 35% or slightly more.

This move to laptops has taken a toll on worldwide desktop shipments. Global desktop volumes continue to increase, thanks mostly to sales in emerging countries, but that percentage is in the low single digits.

Overall, however, the growth differential between desktops and laptops has never been larger. IDC reported that in the third quarter, laptop sales growth was more than 33 percentage points over desktop growth. That differential has not been more than 30% since 1996.

The laptop share of client PCs nearly hit 45% in the third quarter and is expected to reach 50% by the end of 2008 said IDC.

In its Worldwide Quarterly PC Tracker, IDC projects that worldwide PC shipments will increase by 16.7% in the fourth quarter of this year, bolstered by the strong laptop sales. The growth projection is good news for manufacturers, who probably still vividly remember slogging through a slow second half of 2006. PC growth was merely 7.9% in the fourth quarter of 2006.

This fourth quarter is expected to fuel 2007's overall growth rate of 14.6%, up from 10.1% in 2006, IDC reported.

"The peak portable growth seen in the third quarter will be difficult to sustain, but it reflects strong demand across regions and segments that will fuel growth going forward," said Loren Loverde, director of IDC's Worldwide Quarterly PC Tracker, in a statement. "It will be increasingly important for PC vendors to have a strong portable offering to stay competitive as the market continues its rapid shift to mobile computing."

"The significant influences driving the growth of portable PC volume include falling prices, the narrowing performance gap as compared with desktops, improving wireless connectivity, and the expanded access through retail channels," said Richard Shim, personal computing research manager at IDC. "The desktop market will aim to maintain share by emphasizing improvements in energy efficiency, shrinking case designs and emerging mainstream opportunities, such as gaming and all-in-one systems."