Canalys (http://www.canalys.com) says that third quarter (Q3 2011) worldwide computer shipment volumes showed healthy year-on-year growth of 18%. The proliferation of pads drove overall market expansion, though the form factor continued to disrupt traditional desktop, notebook and, in particular, netbook sales, according to the research group.

Total pad shipments were almost three times as many as in the same period a year ago. Notebooks grew 9% and desktops increased 8%, but netbooks declined 28%. Apple’s tablet shipments were up 166%, as sales of the iPad 2 continued to gain momentum, though its share of the worldwide market fell from 96% in Q3 2010 to 67% in Q3 2011 as a result of increasing competition from vendors such as Samsung, Asus and Acer.

Canalys predicts further market share erosion next quarter, despite strong holiday sales. Apple sold 11 million iPads in the last quarter and this strong performance kept it firmly in second place in the total computer market with a 15% share, behind HP (16%) and ahead of Lenovo (12%), Dell (10%) and Acer (10%). Apple maintained a top-two position in each region.

“Ongoing legal and media battles between Apple and its current closest competitor, Samsung, kept the top two pad vendors in the spotlight over the course of Q3,” says Canalys Analyst Tim Coulling. “The result is that the pad market is being portrayed as very much a two-vendor race, with Samsung benefitting the most from the extra publicity on the global stage. In reality though, competition is intensifying as more vendors enter the market and seek to capitalize on growth opportunities.”

As the holiday season gets underway, Canalys expects Amazon to make a major impact with its new Kindle Fire, priced aggressively at US$199. Canalys predicts that the combination of a low price point and extensive video, audio and other content will propel Kindle Fire shipments to more than two million in the fourth quarter, with Amazon taking second place in the United States. A mass upgrade movement from the original Kindle e-book reader to the Fire, however, is not a foregone conclusion and international roll-out has yet to be announced, notes the research gorup.

“HP’s fire sale of the TouchPad, slashing prices from $499 to $99, following its decision to withdraw webOS hardware, demonstrated that pricing is a critical factor in determining success,” says Coulling. “Overall, HP took fifth place in the worldwide pad market, shipping around 560,000 units.”