Apple overtook Hewlett-Packard as the world's largest vendor of personal computers in the fourth quarter for 2011, helped by increasing demand for its iPads,a new market research report determined..

Apple, based in Cupertino, Calif., shipped more than 15 million iPads and 5 million Macs, representing 17 percent of the total 120 million client PCs shipped globally in the fourth quarter, Canalys stimated.

Hewlett-Packard, based in Palo Alto, Calif., was a distant No. 2 with about 12.7 percent. Also it is expected that HP will continue to struggle against Apple's success since the TouchPad is already shelved.

Lenovo Group of China  continued to close the gap on HP, thanks to successful investment outside of core markets. Del, based in Roun Rock, Tex., placed fourth among the top five PC vendors, followed by Acer Group of Taiwan.

While Apple had a six-point gain over the same quarter a year ago HP, Acer, and Dell lost market share. Among the other top five PC vendors, only Lenovo managed to increase its market share, by a relatively modest two points.

In the current year Seattle-based Amazon could also be expected to break into the list of top five PC vendors with its Kindle Fire tablet already garnering huge demand in the market. At the same time Apple might retain its lead if it introduces an iPad 3 tablet in coming monrhs.