Android OS

Android is an operating system for mobile devices such as smartphones and tablet computers. It is developed by the Open Handset Alliance led by Google.

Google purchased the initial developer of the software, Android Inc., in 2005. The unveiling of the Android distribution on November 5, 2007 was announced with the founding of the Open Handset Alliance, a consortium of 84 hardware, software, and telecommunication companies devoted to advancing open standards for mobile devices. Google released most of the Android code under the Apache License, a free software license. The Android Open Source Project (AOSP) is tasked with the maintenance and further development of Android.

Android consists of a kernel based on the Linux kernel, with middleware, libraries and APIs written in  C and application software running on an application framework which includes Java-compatible libraries based on Apache Harmony. Android uses the Dalvik virtual machine with just-in-time compilation to run Dalvik bytecode, which is usually translated from Java bytecode. Android has a large community of developers writing applications ("apps") that extend the functionality of the devices. Developers write primarily in a customized version of Java. There are currently approximately 300,000 apps available for Android, from a total of 500,000 apps over the life of Android. Apps can be downloaded from third-party sites or through online stores such as Android Market, the app store run by Google.

Version history

Android has seen a number of updates since its original release, each fixing bugs and adding new features. Each version is named, in alphabetical order, after a dessert.

Recent releases

• 2.3 Gingerbread refined the user interface, improved the soft keyboard and copy/paste features, improved gaming performance, added   SIP  support (VoIP calls), and added support for Near Field Communication. Android 2.3 Gingerbread is the latest Android version that is available to phones.
•  3.0 Honeycomb was a tablet-oriented release which supports larger screen devices and introduces many new user interface features, and supports multi-core processors and hardware acceleration for graphics. The first device featuring this version, the Motorola Xoom tablet, went on sale in February 2011.  
•   3.1 Honeycomb, released in May 2011, added support for extra input devices, USB host mode for transferring information directly from cameras and other devices, and the Google Movies and Books apps. 
•   3.2 Honeycomb, released in July 2011, added optimization for a broader range of screen sizes, new "zoom-to-fill" screen compatibility mode, loading media files directly from SD card, and an extended screen support API. Huawei Media Pad is the first 7 inch tablet to use this version

• 4.0 Ice Cream Sandwich, announced on October 19, 2011, brought Honeycomb features to smartphones and added new features including facial recognition unlock, network data usage monitoring and control, unified social networking contacts, photography enhancements, offline email searching, and information sharing using NFC.

Design

Linux

Android's kernel is a fork of the Linux kernel but has further architecture changes by Google outside the typical Linux kernel development cycle. Android does not have a native X Window System nor does it support the full set of standard GNU libraries, and this makes it difficult to port existing Linux applications or libraries to Android.

Certain features Google contributed back to the kernel, notably a power management feature called wakelocks, were rejected by mainline kernel developers, partly because kernel maintainers felt that Google did not show any intent to maintain their own code. Even though Google announced in April 2010 that they would hire two employees to work with the Linux kernel community, Greg Kroah-Hartman, the current Linux kernel maintainer for the -stable branch, said in December 2010 that he was concerned that Google was no longer trying to get their code changes included in mainstream Linux Some Google Android developers hinted that "the Android team was getting fed up with the process", because they were a small team and had more urgent work to do on Android. However, in September 2010 Linux kernel developer Rafael J. Wysocki added a patch that improved the mainline Linux wakeup events framework. He said that Android device drivers that use wakelocks can now be easily merged into mainline Linux, but that Android's opportunistic suspend features should not be included in the mainline kernel. In 2011 Linus Torvalds said that "eventually Android and Linux would come back to a common kernel, but it will probably not be for four to five years."