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 lowlevel
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 application to run in its own process, with its own instance of the Dalvik virtual
machine (Android applications are compiled into 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.