Android Mobile Operating System (OS)

Android Versions

Android is a mobile operating system (OS) based on the Linux kernel and currently developed by Google. With a user interface based on direct manipulation, Android is designed primarily for touchscreen mobile devices such as smartphones and tablet computers, with specialized user interfaces for televisions (Android TV), cars (Android Auto), and wrist watches (Android Wear). The OS uses touch inputs that loosely correspond to real-world actions, like swiping, tapping, pinching, and reverse pinching to manipulate on-screen objects, and a virtual keyboard. Despite being primarily designed for touchscreen input, it also has been used in game consoles, digital cameras, regular PCs (e.g. the HP Slate 21) and other electronics.

Android is the most widely used mobile OS and, as of 2013, the highest selling OS overall. Android devices sell more than Windows, iOS, and Mac OS X devices combined,with sales in 2012, 2013 and 2014 close to the installed base of all PCs.As of July 2013 the Google Play store has had over 1 million Android apps published, and over 50 billion apps downloaded.A developer survey conducted in April–May 2013 found that 71% of mobile developers develop for Android.At Google I/O 2014, the company revealed that there were over 1 billion active monthly Android users, up from 538 million in June 2013.
Android's source code is released by Google under open source licenses, although most Android devices ultimately ship with a combination of open source and proprietary software.Initially developed by Android, Inc., which Google backed financially and later bought 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.
Android is popular with technology companies which require a ready-made, low-cost and customizable operating system for high-tech devices. Android's open nature has 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. The operating system's success has made it a target for patent litigation as part of the so-called "smartphone wars" between technology companies.

Firmware History and Development:

Android, Inc. was founded in Palo Alto, California in October 2003 by Andy Rubin (co-founder of Danger),Rich Miner (co-founder of Wildfire Communications, Inc.),Nick Sears (once VP at T-Mobile),and Chris White (headed design and interface development at WebTV) to develop, in Rubin's words, "smarter mobile devices that are more aware of its owner's location and preferences".The early intentions of the company were to develop an advanced operating system for digital cameras, when it was realized that the market for the devices was not large enough, and diverted their efforts to producing a smartphone operating system to rival those of Symbian and Windows Mobile.Despite the past accomplishments of the founders and early employees, Android Inc. operated secretly, revealing only that it was working on software for mobile phones.That same year, Rubin ran out of money. Steve Perlman, a close friend of Rubin, brought him $10,000 in cash in an envelope and refused a stake in the company.
Google acquired Android Inc. on August 17, 2005; key employees of Android Inc., including Rubin, Miner, and White, stayed at the company after the acquisition.Not much was known about Android Inc. at the time, but many assumed that Google was planning to enter the mobile phone market with this move.At Google, the team led by Rubin developed a mobile device platform powered by the Linux kernel. Google marketed the platform to handset makers and carriers on the promise of providing a flexible, upgradable system. Google had lined up a series of hardware component and software partners and signaled to carriers that it was open to various degrees of cooperation on their part.

Since April 2009, Android versions have been developed under a confectionery-themed code name and released in alphabetical order; the exceptions are versions 1.0 and 1.1 as they were not released under specific code names:

Alpha (1.0)
Beta (1.1)
Cupcake (1.5)
Donut (1.6)
Eclair (2.0–2.1)
Froyo (2.2–2.2.3)
Gingerbread (2.3–2.3.7)
Honeycomb (3.0–3.2.6)
Ice Cream Sandwich (4.0–4.0.4)
Jelly Bean (4.1–4.3.1)
KitKat (4.4–4.4.4)
Lollipop (5.0)

Pre-commercial release versions (2007–2008)

Alpha
There were at least two internal releases inside Google and the OHA before the Beta was released in November 2007. For the milestones in internal releases, names of fictional robots were chosen, with various releases code-named "Astro Boy", "Bender" and "R2-D2". Dan Morrill created some of the first mascot logos, but the current green Android logo was designed by Irina Blok.The project manager, Ryan Gibson, conceived of the confections naming scheme that has been used for the majority of the public releases, starting with Android 1.5.

Beta
The Beta was released on November 5, 2007, while the software development kit (SDK) was released on November 12, 2007. The November 5 date is popularly celebrated as Android's "birthday".Public beta versions of the SDK were released in the following order:

November 16, 2007: m3-rc22a
December 14, 2007: m3-rc37a
February 13, 2008: m5-rc14
March 3, 2008: m5-rc15
August 18, 2008: 0.9
September 23, 2008: 1.0-r1

Version history by API level

Android 1.0 (API level 1)
Android 1.1 (API level 2)
Android 1.5 Cupcake (API level 3)
Android 1.6 Donut (API level 4)
Android 2.0 Eclair (API level 5)
Android 2.0.1 Eclair (API level 6)
Android 2.1 Eclair (API level 7)
Android 2.2–2.2.3 Froyo (API level 8)
Android 2.3–2.3.2 Gingerbread (API level 9)
Android 2.3.3–2.3.7 Gingerbread (API level 10)
Android 3.0 Honeycomb (API level 11)
Android 3.1 Honeycomb (API level 12)
Android 3.2 Honeycomb (API level 13)
Android 4.0–4.0.2 Ice Cream Sandwich (API level 14)
Android 4.0.3–4.0.4 Ice Cream Sandwich (API level 15)
Android 4.1 Jelly Bean (API level 16)
Android 4.2 Jelly Bean (API level 17)
Android 4.3 Jelly Bean (API level 18)
Android 4.4 KitKat (API level 19)
Android 4.4 KitKat with wearable extensions (API level 20
Android 5.0 Lollipop (API level 21)

Android 5.0 "Lollipop" was unveiled under the codename "Android L" on June 25, 2014 during Google I/O, and became available as official over-the-air (OTA) updates on November 12, 2014 for select devices that run distributions of Android serviced by Google, including Nexus and Google Play edition devices. Its source code was made available on November 3, 2014.
Lollipop brings a redesigned user interface built around a responsive design language referred to as "material design". Other changes include improvements to the notifications, which can be accessed from the lockscreen and displayed within applications as top-of-the-screen banners. Google also made internal changes to the platform, with the Android Runtime (ART) officially replacing Dalvik for improved application performance, and with changes intended to improve and optimize battery usage, known internally as Project Volta.