The primary source for Worldometers statistics on PC sales is provided by Gartner.
Additional source for this data is IDC, the premier global provider of market intelligence, advisory services, and events for the information technology, telecommunications, and consumer technology markets.
IDC's Worldwide Quarterly PC Tracker gathers PC market data in 55 countries by vendor, form factor, brand, processor brand and speed, sales channel and user segment. The research includes historical and forecast trend analysis as well as price band and installed base data.
The PC tracker includes Desktop, Notebook, Ultra Portable, and x86 Server market data. It does not include handhelds.
According to Gartner Dataquest's statistics, in April 2002 the billionth personal computer was shipped. The second billion mark was supposedly reached in 2007.
But how many computers are actually in use? According to a report by Forrester Research, there were over one billion PCs in use worldwide by the end of 2008, and over 2 billion by the year 2015.
References and useful links: