Introduction to Android

Android is a software development stack includes operating system, middleware technology and application frameworks

Android is a Linux-based operating system for mobile devices like smart phones and tablets.

Android is developed by the Open Handset Alliance. Google purchased the Android from the initial developer Android Inc.  in year 2005. Google released the Android code as open source under Apache License.

Android Architecture

The Android stack is divided in four major layers.

 Linux Kernel Layer– The core layer of the android operating system is the Linux kernel. The core layer provides the interface between hardware layer and software layers. The security, memory management, user process management, network and driver management is handled at this layer. The Android is based on Linux kernel 2.6.

 Android Runtime and Core Library Layer – This Layer provides a Dalvik Virtual Machine and core set of libraries to run the JAVA applications. The Dalvik VM executes the .dex (Dalvik executable) files. The Dalvik VM is optimized to run the small footprint of applications at fast speed.

Each of application runs its own process on Linux kernel and run a different instance of Dalvik VM.

Android includes a set of C/ C++ libraries used by various components of the Android Platform. These libraries could be accessible by developers using standard application frameworks.

Library	Description
C System Library (libc)	Optimized library for embedded Linux devices
Media libraries	Libraries to support playback and recording of many popular audio and video formats, as well as static image files, including MPEG4, H.264, MP3, AAC, AMR, JPG, and PNG
Surface Manager	Manage access to the display subsystem
LibWebCore	Web browser engine to manage the web views
SGL	2D graphics engine
3D Libraries	OpenGL ES 1.0 3D libraries for high quality 3D raster graphics
Free Type	Bitmap and Vector Font Rendering
SQLLite	Lightweight relational database with SQL access

Application Framework Layer – Application Framework Layer provides a set of frameworks to access the android run-time libraries and core functions to create and manage the user interface, run background jobs, set notifications and alarms. The components re-usability provides a flexible application development with framework layer. The application architecture allows the application to publish its features to other applications.

At high level the android system provides the following set of system services

·         A rich and extensible set of views used to build the user interfaces for applications

·         Content Providers to share and access the data between applications.

·         A Resource Manager to manage the resources

·         A Notification Manager to display the alerts and notifications on status bar

·         An Activity Manager to manage the lifecycle of application and state management

The top layer is the application layer where lot of applications are bundled with platform and developers can build their own applications.

See the bellow the Android Architecture Diagram

Android Architecture