Gartner reports that the number of PCs worldwide has surpassed one billion units.

The installed base of PCs is growing just under 12% annually which means if the same pace, the number of PCs in the world will surpass two billion units by early-2014.

The majority of the world's PCs remain concentrated in mature markets but - as with the mobile phone industry - emerging markets will claim an increasingly larger share of the world's installed base going forward.

"Mature markets such as the United States, Western Europe, and Japan currently account for 58% of the world's installed PCs, but these markets only account for 15% of the world's population", said a research director at Gartner.

"We expect per capita PC penetration in emerging markets to double by 2013."

Gartner also looked at how often PCs are replaced and forecasts that just over 180 million PCs, around 16% of existing computers - will be replaced this year.

The warning is that a fifth of these, or some 35 million PCs, will be dumped into landfill with little or no regard for their toxic content.