Google Android Operating System

Android is a Linux-based operating system designed primarily for touchscreen mobile devices such as smartphones and tablet computers. Initially developed by Android, Inc., whom Google financially backed and later purchased in 2005, Android was unveiled in 2007 along with the founding of the Open Handset Alliance: a consortium of hardware, software, and telecommunication companies devoted to advancing open standards for mobile devices.The first Android-powered phone was sold in October 2008.

Android is open source and Google releases the code under the Apache License. This open source code and permissive licensing allows the software to be freely modified and distributed by device manufacturers, wireless carriers and enthusiast developers. Additionally, Android has a large community of developers writing applications ("apps") that extend the functionality of devices, written primarily in a customized version of the Java programming language. In October 2012, there were approximately 700,000 apps available for Android, and the estimated number of applications downloaded from Google Play, Android's primary app store, was 25 billion.

These factors have allowed Android to become the world's most widely used smartphone platform and the software of choice for technology companies who require a low-cost, customizable, lightweight operating system for high tech devices without developing one from scratch. As a result, despite being primarily designed for phones and tablets, it has seen additional applications on televisions, games consoles and other electronics. Android's open nature has further encouraged a large community of developers and enthusiasts to use the open source code as a foundation for community-driven projects, which add new features for advanced users or bring Android to devices which were officially released running other operating systems.

Android had a worldwide smartphone market share of 75% during the third quarter of 2012, with 500 million devices activated in total and 1.3 million activations per day. The operating system's success has made it a target for patent litigation as part of the so-called "smartphone wars" between technology companies.

      

The source code for Android is available under free and open source software licenses. Google publishes most of the code (including network and telephony stacks) under the Apache License version 2.0, and the rest, Linux kernel changes, under the GNU General Public License version 2. The Open Handset Alliance develops the changes to the Linux kernel, in public, with source code publicly available at all times. The rest of Android is developed in private by Google, with source code released publicly when a new version is released. Typically Google collaborates with a hardware manufacturer to produce a 'flagship' device (part of the Google Nexus series) featuring the new version of Android, then makes the source code available after that device has been released.

In early 2011, Google chose to temporarily withhold the Android source code to the tablet-only 3.0 Honeycomb release. The reason, according to Andy Rubin in an official Android blog post, was because Honeycomb was rushed for production of the Motorola Xoom, and they did not want third parties creating a "really bad user experience" by attempting to put onto smartphones a version of Android intended for tablets. The source code was once again made available in November 2011 with the release of Android 4.0.

Even though the software is open-source, device manufacturers cannot use Google's Android trademark unless Google certifies that the device complies with their Compatibility Definition Document (CDD). Devices must also meet this definition to be eligible to license Google's closed-source applications, including Google Play. As Android is not completely released under a GPL compatible license, e.g. Google's code is under the Apache license, and also because Google Play allows proprietary software, Richard Stallman and the Free Software Foundation have been critical of Android and have recommended the usage of alternatives such as Replicant.

Android Versions:

Version	Code Name	Release date	API level	Distribution (December 3, 2012)
4.2	Jelly Bean	November 13, 2012	17	0.8%
4.1	Jelly Bean	July 9, 2012	16	5.9%
4.0.x	Ice Cream Sandwich	December 16, 2011	15	27.5%
3.2	Honeycomb	July 15, 2011	13	1.2%
3.1	Honeycomb	May 10, 2011	12	0.4%
2.3.3–2.3.7	Gingerbread	February 9, 2011	10	50.6%
2.3–2.3.2	Gingerbread	December 6, 2010	9	0.2%
2.2	Froyo	May 20, 2010	8	10.3%
2.0–2.1	Éclair	October 26, 2009	7	2.7%
1.6	Donut	September 15, 2009	4	0.3%
1.5	Cupcake	April 30, 2009	3	0.1%