Sunday, 13 January 2013

Android Architecture


Linux Kernel:
Android relies on Linux version 2.6 for core system services such as security, memory management, process management, network stack, and driver model. The kernel also acts as an abstraction layer between the hardware and the rest of the software stack.

Android  Runtime:
Android includes a set of core libraries that provides most of the functionality available in the core libraries of the Java programming language.
Every Android application runs in its own process, with its own instance of the Dalvik virtual machine. Dalvik has been written so that a device can run multiple VMs efficiently. The Dalvik VM executes files in the Dalvik Executable (.dex) format which is optimized for minimal memory footprint. The VM is register-based, and runs classes compiled by a Java language compiler that have been transformed into the .dex format by the included "dx" tool.
The Dalvik VM relies on the Linux kernel for underlying functionality such as threading and low-level memory management.
Libraries:
Android includes a set of C/C++ libraries used by various components of the Android system. These capabilities are exposed to developers through the Android application framework. Some of the core libraries are listed below:
·       Free Type: This library supports bitmap and vector font rendering.
·       Libc: This library is a BSD-derived implementation of standard c system library, tuned for embedded linux-based devices.
·       LibWebCare: This library offers a modern and fast web browser engine that powers the Android browser and an embedded web view . Its based on WebKit and is also used by the Google Chrome and Apple Safari browsers.
·       Media Framework: These libraries ,which are based on packet video’s OpenCORE , support the playback and recording of many  popular audio and video formats, as well as working with static image files.
·       OpenGL/ES: These 3D Graphics libraries provide an OpenGL implementation based on OpenGL/ES 1.0 APIs.
·       SGL: This library provides the underlying 2D Graphics engine.
·       SQLite: This library provides a powerful and lightweight relational database engine that’s available for all app’s and also used by Mozilla Firefox and Apple’s iPhone for persistent storage.
·       SSL: This library provides secure sockets layer-based (SSL-based) security for network communication.
·       Surface Manager: This library manages access to the display subsystem , and seamlessly composites 2D and 3D graphic layers from multiple apps.
Application Framework:
By providing an open development platform, Android offers developers the ability to build extremely rich and innovative applications. Developers are free to take advantage of the device hardware, access location information, run background services, set alarms, add notifications to the status bar, and much, much more.Developers have full access to the same framework APIs used by the core applications. The application architecture is designed to simplify the reuse of components; any application can publish its capabilities and any other application may then make use of those capabilities (subject to security constraints enforced by the framework). This same mechanism allows components to be replaced by the user.
Underlying all applications is a set of services and systems, including:
·       A rich and extensible set of Views that can be used to build an application, including lists, grids, text boxes, buttons, and even an embeddable web browser
·       Content Providers that enable applications to access data from other applications (such as Contacts), or to share their own data
·       A Resource Manager, providing access to non-code resources such as localized strings, graphics, and layout files
·       A Notification Manager that enables all applications to display custom alerts in the status bar
·       An Activity Manager that manages the lifecycle of applications and provides a common navigation backstack

Applications:
Android will ship with a set of core applications including an email client, SMS program, calendar, maps, browser, contacts, and others. All applications are written using the Java programming language.