Architecture of Android

In order to understand how Android works, take a look at Figure 1-1, which shows the various layers that make up the Android operating system  (OS).


The Android OS is roughly divided into five sections in four main layers:

➤      Linux kernel — This is the kernel on which Android is based. This layer contains all  the low- level device drivers for the various hardware components of an Android  device.

➤      Libraries — These contain all the code that provides the main features of an Android   OS. For example, the SQLite library provides database support so that an application can use it for  data storage. The WebKit library provides functionalities for web   browsing.

➤      Android runtime — At the same layer as the libraries, the Android runtime provides a set of core libraries that enable developers to write Android apps using the Java programming language. The Android runtime also includes the Dalvik virtual machine, which enables every Android appli- cation to run in its own process, with its own instance of the Dalvik virtual machine (Android applications are compiled into the Dalvik executables). Dalvik is a specialized virtual machine designed specifically for Android and optimized for battery-powered mobile devices with limited memory and CPU.

➤      Application framework — Exposes the various capabilities of the Android OS to application developers so that they can make use of them in their  applications.

➤      Applications — At this top layer, you will find applications that ship with the Android device (such as Phone, Contacts, Browser, etc.), as well as applications that you download and install from the Android Market. Any applications that you write are located at this   layer.

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