Gartner has lowered its PC unit forecast for 2011 and 2012 based on expectations of weaker demand in the face of devices such as iPad.

Worldwide PC shipments are forecast to reach 387.8 million units in 2011, a 10.5% increase from 2010.

But this is now down from Gartner's previous projection of 15.9% growth this year.

Gartner expects worldwide PC shipments to total 440.6 million units in 2012, a 13.6% increase from 2011 but still down from the previous figure of 14.8%.

Analysts say that consumer mobile PCs have been the growth engine of the PC market over the past five years.

But due to the spread of low-cost embedded wi-fi deices, consumers can access the internet increasingly more without a PC.

"We expect growing consumer enthusiasm for mobile PC alternatives, such as the iPad and other media tablets, to dramatically slow home mobile PC sales, especially in mature markets," said research director, George Shiffler.

"We once thought that mobile PC growth would continue to be sustained by consumers buying second and third mobile PCs as personal devices. However, we now believe that consumers are not only likely to forgo additional mobile PC buys but are also likely to extend the lifetimes of the mobile PCs they retain as they adopt media tablets and other mobile PC alternatives as their primary mobile device. Overall, we now expect home mobile PCs to average less than 10% annual growth in mature markets from 2011 through 2015."