If the iPad is considered a mobile PC, then Apple is now the top mobile PC vendor in the U.S. and the third largest in the world thanks to its popular tablet, according to data released yesterday by DisplaySearch.

Over the third quarter, Apple was able to grab a 12.4 share of mobile PC shipments around the world, with the iPad accounting for two-thirds (8 percent) of those devices, according to the new "DisplaySearch Quarterly Mobile PC Shipment and Forecast Report."

Of course, some may disagree with DisplaySearch calling the iPad a mobile PC and lumping it in with notebooks and Netbooks. Leaving out the iPad, Apple recently became the third largest overall PC vendor in the U.S. behind Hewlett-Packard and Dell, according to IDC. But DisplaySearch's numbers still point to the clear impact of the tablet on Apple's market share.

Though other tech players have been busy launching and prepping their own tablet PCs, the iPad continues to dominate the landscape. Apple sold more than 3 million iPads in the first three months. Bernstein Research retail analyst Colin McGranahan projected in early October that Apple would capture around $12 billion in global iPad sales for the year, and almost $20 billion next year.

Of all iPad shipments in the third quarter, 95 percent were directed to developed markets, mainly North America, according to DisplaySearch. McGranahan told CNET in October he believes 45 percent of the tablet's sales are in the United States.

But the iPad's booming business in North America also points to a weakness in certain other countries, notably Japan, says DisplaySearch. The lack of language-specific content and apps has slowed the adoption of the tablet in normally tech-savvy Japan. The iPad may also face a tough road in less developed regions.

"On a global scale, the adoption of iPad is not without its challenges," Hidetoshi Himuro, director of IT market research at DisplaySearch, said in a statement. "Localized content in non-English speaking regions is sparse, and iPad owners must have a PC for downloading content from iTunes. As a result, penetration in developing regions will be slow."

That could open opportunities for other tablet vendors to reach local consumers in different countries.

"As other players come to market with tablet PCs it will be interesting to see if they can move beyond the Western-centric nature of Apple's product and develop an infrastructure to support local needs, especially with the growth of consumer spending in China on personal computing devices," Chris Connery, vice president of large-format displays at DisplaySearch, said in a statement.

Looking beyond the iPad at other mobile PC vendors, HP was still the global leader in the third quarter with a 17.3 percent share and 9.5 million mobile PCs shipped. But Acer trailed closely with a 16.5 share and 9.1 million units shipped.

Overall, global shipments of mobile PCs (including tablets) hit 55 million in the third quarter, a gain of 19 percent from the prior year's quarter and the highest volume since DisplaySearch started tracking the market in 1999.