Apple claimed some 9.4% market share in the U.S. computer market, according to research firm IDC. The firm's data pegged Apple's Mac unit sales during the quarter at 1.64 million for the U.S., an 11.8% increase from the year ago quarter. This lies in contrast with quarterly numbers issued by Gartner Wednesday putting Apple's unit sales at 1.47 million Macs for 8.8% market share.

Overall, IDC said that unit sales increased in the U.S. by 2.5%, propelled in part by increased sales of cheap portable computers and back-to-school purchases. The firm also said that companies with a strong retail presence were the "main beneficiaries" of the increased sales. Apple, for instance, has a very strong retail presence in the form of its fleet of Apple Stores, though IDC did not single Apple out by name.

"Despite the ongoing mix of gloom and caution on the economic front, the PC market continues to rebound quickly," Loren Loverde, program director for IDC's Tracker Program, said in a statement. "The competitive landscape, the transition to portables, new and low-power designs, growth in retail and consumer segments, and the impact of falling prices are all reflected in the gains by HP and Acer, as well as overall market growth."

September sales table for the U.S. computer market
Table provided by IDC

IDC said that worldwide global unit sales increased by 2.3%, and like Gartner, said that such an increase is significant after three consecutive quarters of declining unit sales.

The firm also said that, "Seeing market growth ahead of the launch of Microsoft's Windows 7 bodes very well for the fourth quarter and next year." This stands in direct contrast to Gartner's report, where the company said, "Windows 7 should have a minimal impact on PC unit growth."

HP claimed the top spot on IDC's global sales, with 15.78 million PCs sold and 20.2% market share. That's well ahead of new #2 Acer with 10.95 million PCs sold and 14% market share. Former #1 Dell came in third this quarter with 9.95 million PCs sold and 12.7% market share.

As with Gartner, Apple doesn't make the Top 5 in IDC's report for global sales.