Android

Editor's Notes

1. Linux KernelThe basic layer is the Linux kernel.made by linustorwalds. 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.LibrariesThe 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 formatsSQLite: SQLite is the database engine used in android for data storage purposesWebKit: It is the browser engine used to display HTML contentOpenGL: Used to render 2D or 3D graphics content to the screenAndroid RuntimeAndroid Runtime consists of Dalvik Virtual machine and Core Java libraries.Dalvik Virtual MachineIt 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 LibrariesThese are different from Java SE and Java ME libraries. However these libraries provides most of the functionalities defined in the Java SE libraries.Application FrameworkThese 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 applicationsContent Providers: Manage the data sharing between applicationsTelephony 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 towerResource Manager: Manage the various types of resources we use in our ApplicationApplicationsApplications 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 appDialerWeb browserContact managerAs a developer we are able to write an app which replace any existing system app. That is, you are not limited in accessing any particular feature. You are practically limitless and can whatever you want to do with the android (as long as the users of your app permits it). Thus Android is opening endless opportunities to the developer.