There are an estimated over 1 billion PCs installed worldwide and the number is expected to surpass 2-billion by early 2014 (a 12 percent yearly increase), reveals Gartner in its latest report.

The installed base of PCs, Gartner says, is the estimated number of PCs in use as opposed to the number of PCs shipped over a given period.

And the installed base of PCs remains heavily concentrated in mature markets. Markets such as the United States, Western Europe, and Japan currently account for 58 percent of the world's installed base of PCs; yet they also account for just 15 percent of the world's population, as per Gartner.

The report does however say that going forward, emerging markets will claim an increasingly larger share of the installed PC base. The reason being rapidly rising PC penetration in these markets, that would continue to drive double-digit PC growth.

Meanwhile, the global installed PC base is constantly being churned as PC users replace older machines with newer ones, older machines (at least some of them) find their way back to second owners through various channels, and the rest get dismantled and recycled or simply dumped into landfills.

Meike Escherich, principal research analyst at Gartner, estimates, "Just over 180 million PCs, which is approximately 16 percent of the existing installed base will be replaced this year. A fifth of these, or some 35 million PCs, will be dumped into landfill with little or no regard for their toxic content."

Which brings us to one more very important issue (call it the by-product of large-scale proliferation of PCs if you like): as Escherich adds, "The disposition of retired PCs has become a high-profile issue for many PC vendors, governments and environmental interest groups. It will become an even more pressing issue, especially in emerging markets, as the number of retired PCs grows with the continuing expansion of the PC installed base."