Android Architecture
· The following diagram shows the various layers that make up the Android operating system (OS).
· Linux Kernel:
Ø Android relies on Linux version 2.6 for core system services such as security, memory management, process management, network stack, and driver model.
Ø The kernel also acts as an abstraction layer between the hardware and the rest of the software stack.
· Android Runtime:
Ø Core Libraries: Android includes a set of core libraries that provides most of the functionality available in the core libraries of the Java programming language.
Ø Dalvik Virtual machine:
üEvery Android application runs in its own process, with its own instance of the Dalvik virtual machine.
üDalvik 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.
üThe 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.
üThe Dalvik VM relies on the Linux kernel for underlying functionality such as threading and low-level memory management.
· Libraries:
Ø 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:
ü System C library - a BSD-derived implementation of the standard C system library (libc), tuned for embedded Linux-based devices
ü Media Libraries - based on PacketVideo's OpenCORE; the libraries support playback and recording of many popular audio and video formats, as well as static image files, including MPEG4, H.264, MP3, AAC, AMR, JPG, and PNG
ü Surface Manager - manages access to the display subsystem and seamlessly composites 2D and 3D graphic layers from multiple applications
ü LibWebCore - a modern web browser engine which powers both the Android browser and an embeddable web view
ü SGL - the underlying 2D graphics engine
ü 3D libraries - an implementation based on OpenGL ES 1.0 APIs; the libraries use either hardware 3D acceleration (where available) or the included, highly optimized 3D software rasterizer
ü FreeType - bitmap and vector font rendering
ü SQLite - a powerful and lightweight relational database engine available to all applications
· Application Framework:
Ø Android offers developers the ability to build extremely rich and innovative applications.
Ø 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.
Ø Full access to the same framework APIs used by the core applications.
Ø 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.
Platform Services Activity Manager | Hardware Services Telephony Service |
Package Manager | Bluetooth Service |
Window Manager | Wi-Fi Service |
Resource Manager | USB Service |
Content Providers | Sensor Service |
View System | |
Ø Applications are the general applications that are pre shipped with the phone or downloaded and installed from the market.
Example:
§ A set of core applications including an email client, SMS program, calendar, maps, browser, contacts, and others.
Ø All applications are written using the Java programming language.
Ø Applications make use of Application Framework.
No comments:
Post a Comment