The number of personal computers in use worldwide will reach 1 billion by 2008 and 2 billion by 2015, with most new users coming from China, Russia, Brazil, and India, according to a new study of computer-adoption trends.

"Worldwide PC Adoption Forecast, 2007 to 2015," a report by Cambridge, Mass.-based Forrester Research, studied the 67 largest emerging and mature markets for PCs based on population. Although it took 27 years from the introduction of IBM's first PC to reach 1 billion users, researchers predict it will take less than seven years to reach the 2 billion mark -- growth that is likely to bring new opportunities and new markets for entrepreneurs in a range of industries.

The largest market for PCs will be China, with close to 500 million new users expected by 2015. Rising personal income levels and significant investments in infrastructure are the basis for this prediction, although the report stressed the need to invest in education in order to sustain the technological gains China has experienced in recent years.

India, Russia and Brazil, the next largest markets, are expected to bring in a combined total of 300 million PC users.

"There is nothing more important to the long-term health of the technology industry -- and personal technology in particular -- than the ability to deliver relevant, accessible, and affordable technology to the billions of people worldwide who have not been exposed to it," Simon Yates, Forrester's vice president and research director, said in a statement.

Some of the factors that will enable such a rapid proliferation of computers include a significant reduction in the price of hardware and software due to new technology, as well as the introduction of wireless Internet access to remote areas that previously had no such connection.

However, researchers warned that selling PCs to emerging markets must follow a much different model from current sales methods. Manufacturers will be forced to sell large volumes of PCs at once, rather than gradually introducing products to the marketplace. In addition, while PC users in more developed countries tend to replace their computers every four or five years, consumers in developing nations are likely to keep their PCs for longer periods. Moreover, many of the large computer manufacturers have not focused a large amount of resources on selling to these emerging markets.

"The industry can probably survive selling incrementally better hardware and software to the people who already have technology in their lives," said Yates, "but the vast majority of growth in the PC and related industries will come from emerging markets."