<P> Android devices account for more than half of smartphone sales in most markets, including the US, while "only in Japan was Apple on top" (September--November 2013 numbers). At the end of 2013, over 1.5 billion Android smartphones have been sold in the four years since 2010, making Android the most sold phone and tablet OS . Three billion Android smartphones are estimated to be sold by the end of 2014 (including previous years). According to Gartner research company, Android - based devices outsold all contenders, every year since 2012 . In 2013, it outsold Windows 2.8: 1 or by 573 million . As of 2015, Android has the largest installed base of all operating systems; Since 2013, devices running it also sell more than Windows, iOS and Mac OS X devices combined . </P> <P> According to StatCounter, which tracks only the use for browsing the web, Android is the most popular mobile operating system since August 2013 . Android is the most popular operating system for web browsing in India and several other countries (e.g. virtually all of Asia, with Japan and North Korea exceptions). According to StatCounter, Android is most used on mobile in all African countries, and it stated "mobile usage has already overtaken desktop in several countries including India, South Africa and Saudi Arabia", with virtually all countries in Africa having done so already (except for seven countries, including Egypt), such as Ethiopia and Kenya in which mobile (including tablets) usage is at 90.46% (Android only, accounts for 75.81% of all use there). </P> <P> While Android phones in the Western world commonly include Google's proprietary add - ons (such as Google Play) to the otherwise open - source operating system, this is increasingly not the case in emerging markets; "ABI Research claims that 65 million devices shipped globally with open - source Android in the second quarter of (2014), up from 54 million in the first quarter"; depending on country, percent of phones estimated to be based only on AOSP source code, forgoing the Android trademark: Thailand (44%), Philippines (38%), Indonesia (31%), India (21%), Malaysia (24%), Mexico (18%), Brazil (9%). </P> <P> According to a January 2015 Gartner report, "Android surpassed a billion shipments of devices in 2014, and will continue to grow at a double - digit pace in 2015, with a 26 percent increase year over year ." This made it the first time that any general - purpose operating system has reached more than one billion end users within a year: by reaching close to 1.16 billion end users in 2014, Android shipped over four times more than iOS and OS X combined, and over three times more than Microsoft Windows . Gartner expected the whole mobile phone market to "reach two billion units in 2016", including Android . Describing the statistics, Farhad Manjoo wrote in The New York Times that "About one of every two computers sold today is running Android . (It) has become Earth's dominant computing platform ." </P>

Write a short note on android operating system