About 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., 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. 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.


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Version	Code Name	Release Date	API Level	Distribution
developer preview 1	N	______________	_______	_______
6.0–6.0.1	Marshmallow	October 5, 2015	23	2.3%
5.0–5.1.1	Lollipop	November 12, 2014	21–22	34.1%
4.4–4.4W.2	KitKat	October 31, 2013	19–20	35.5%
4.1-4.3.1	Jelly Bean	July 9, 2012	16-18	32.5%
4.0.3-4.0.4	IceCreamSendwich	December 16, 2011	4-15	23.3%
3.1	Honeycomb	May 10, 2011	11-13	0%
2.3-2.3.7	Gingerbread	February 9, 2011	9-10	34.1%
2.2-2.2.3	Froyo	May 20, 2010	8	3.1%
2.0-2.1	Eclair	October 26, 2009	7	1.4%
1.6	Donut	September 15, 2009	4	0.1%
1.5	Cupcake	April 15, 2009	3	0%

Android phones and tablets aren’t all kept up-to-date with the current version of Android. It’s often helpful to know which version of Android a specific phone or tablet is running so you can get help with something or determine whether a feature is present.

Normally you can check Android version by going  Settings-Scroll down on the Settings screen and look for an “About phone” or “About tablet” option. You’ll usually find this at the very bottom of the main Settings screen, under System. Look for “Android version” to find the version of Android installed on your device.

It just displays the version number, not the code name — for example, it says “Android 6.0” instead of “Android 6.0 Marshmallow”. You’ll have to perform a web search or look up a list of Android code names if you want to know the code name associated with the version. prefer above Table to find out which version is yours if you don't know.

Also you can see some differences like icons and default wallpaper in various android version main screens. But its also consist about your device company. 

some examples for different android main screens