History of Android and Android OS Architecture

History Of Android  

      Android is a Linux-based open source software stack  that comes along with operating system , middle ware, native mobile applications, along with set of API libraries for building third party applications. It was designed primarily for touchscreen mobile devices such as smartphones, tablets and now its focus has spread wider across other embedded systems. Initially developed by Android Inc.,(founded in 2003 and is based in Palo Alto, California) which operated as subsidiary of Google and later purchased by Google in 2005.

                Android was publicly announced in 2007 and first phone was sold on October 2008.

              

Android OS Architecture

Android OS consists of four main layers

•  kernel
•  libraries 
•  applications framework 
•  applications.

Kernel Layer

The whole Android OS is built on top of the Linux 2.6 Kernel with some further   architectural changes made by Google.  It is this Linux that interacts with the hardware and contains all the essential hardware drivers. Linux was chosen since it has a proven track record in desktop systems and in many cases doesn’t require drivers to be rewritten. Linux provides such things as virtual memory, networking, drivers, and power management. 

Native libraries layer

The native libraries layer provides Android with the capabilities for its core features. Android is shipped with SGL which acts as the primary 2D graphics renderer. Its counterpart is OpenGL ES which provides 3D graphics support. Android comes packed with SQLite which takes care of most data storage. The WebKit web rendering engine is also shipped with Android and has been tailored to render web pages for smaller screen sizes. Dalvik virtual machine which is a part of this layer. The Dalvik virtual machine is a bytecode interpreter which is highly optimized for executing on the mobile platform. The bytecodes are converted Java binaries that are very quick and efficient to run on smaller processors. The core libraries are written in Java and provide much of the core classes which would normally be available in a Java virtual machine.

 Applications framework Layer

               The applications framework provides all of the major APIs that the applications will use including things like sharing data, accessing the telephony system, and receiving notifications. This layer and the layer above it are written completely in Java. 

Applications layer

This is the top layer in Android architecture. This layer contains software written by the Android team as well as any third-party software that is installed on the device.Even the most core features such as the phone and the contacts application reside in this layer. Any third party developer can access this layer, as an effect of which any events of core android apps can be handled by third party applications