Android Architecture

The above figure shows the diagram of Android Architecture. The Android OS can be referred to as a software stack of different layers, where each layer is a group of sveral  program components. Together it includes operating system, middleware and important applications. Each layer in the architecture provides different services to the layer just above it. We will examine the features of each layer in detail.

Linux Kernel

The basic layer is the Linux kernel.

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. Drivers are programs that control and communicate with the hardware. For example, consider the Bluetooth function. All devices has a Bluetooth hardware in it. Therefore the kernel must include a Bluetooth driver to communicate with the Bluetooth hardware.  The Linux kernel also  acts as an abstraction layer between the hardware and other software layers. Android uses the Linux for all its core functionality such as Memory management, process management, networking, security settings etc. As the Android is built on a most popular and proven foundation, it made the porting of Android to variety of hardware, a relatively painless task.

Libraries

The next layer is the Android’s native libraries.

It is this layer that enables the device to handle different types of data. These libraries are written in c or c++ language and are specific for a particular hardware.

Some of the important native libraries include the following:

Surface Manager: 

It is used for compositing window manager with off-screen buffering. Off-screen buffering means you cant directly draw into the screen, but your drawings go to the off-screen buffer. There it is combined with other drawings and form the final screen the user will see. This off screen buffer is the reason behind the transparency of windows.

Media framework: 

Media framework provides different media codecs allowing the recording and playback of different media formats.

SQLite: 

SQLite is the database engine used in android for data storage purposes

WebKit:

It is the browser engine used to display HTML content

OpenGL:

Used to render 2D or 3D graphics content to the screen

Android Runtime

Android Runtime consists of Dalvik Virtual machine and Core Java libraries.

Dalvik Virtual Machine

It is a type of JVM used in android devices to run apps and is optimized for low processing power and low memory environments. Unlike the JVM, the Dalvik Virtual Machine doesn’t run .class files, instead it runs .dex files. .dex files are built from .class file at the time of compilation and provides hifger efficiency in low resource environments. The Dalvik VM allows multiple instance of Virtual machine to be created simultaneously providing security, isolation, memory management and threading support. It is developed by Dan Bornstein of Google.

Core Java Libraries

These are different from Java SE and Java ME libraries. However these libraries provides most of the functionalities defined in the Java SE libraries.

Application Framework

These are the blocks that our applications directly interacts with. These programs manage the basic functions of phone like resource management, voice call management etc. As a developer, you just consider these are some basic tools with which we are building our applications.

Important blocks of Application framework are:

Activity Manager: 

Manages the activity life cycle of applications

Content Providers:

 Manage the data sharing between applications

Telephony Manager: 

Manages all voice calls. We use telephony manager if we want to access voice calls in our application.

Location Manager: 

Location management, using GPS or cell tower

Resource Manager: 

Manage the various types of resources we use in our Application

Applications

Applications are the top layer in the Android architecture and this is where our applications are gonna fit.

 Several standard applications comes pre-installed with every device, such as:

• SMS client app
• Dialer
• Web browser
• Contact manager

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