Android is an open-source, Linux-based operating system designed primarily for mobile devices such as smartphones and tablets. To ensure flexibility, scalability, and security, Android follows a layered architecture, where each layer provides services to the layer above it. It helps developers know how applications interact with system components and hardware.
Android architecture is divided into the following main layers:
1. Applications Layer
The Applications layer is the topmost layer of Android architecture. It includes both system applications that come preinstalled on the device and third-party applications installed by users from app stores or other sources. Examples of system applications includes Settings while Whatsapp is the example of third- party applications. Because of this layered design:
- Developers can focus on building features without worrying about hardware details.
- Applications remain portable across different Android devices.
- The system maintains better security and resource management.
2. Application Framework
The Android team has built on a known set of proven libraries, built in the background, and all of it is exposed through Android interfaces. These interfaces wrap up all the various libraries and make them useful for the Developer. They don’t have to build any of the functionality provided by the android. Some of these interfaces include:
- Activity Manager: Manages the lifecycle of applications and activities.
- Window Manager: Handles windows and screen layouts.
- Content Providers: Allow applications to share data with other applications.
- Resource Manager: Manages resources such as strings, layouts, and images.
- Notification Manager: Handles notifications displayed in the status bar.
3. Android Runtime
It is the third section of the architecture. It provides one of the key components which is called Dalvik Virtual Machine. It acts like Java Virtual Machine which is designed especially for Android. Android uses its own custom VM designed to ensure that multiple instances run efficiently on a single device. Key features are:
- Each application runs in its own process.
- Each process has its own virtual machine.
- Provides core Java libraries required by applications.
ART improves performance by using Ahead-of-Time (AOT) and Just-in-Time (JIT) compilation techniques.
4. Native Libraries
Android includes a set of native C/C++ libraries that provide essential functionalities to the system. Some commonly used libraries:
- SQLite: A lightweight relational database engine used for local data storage in Android applications.
- OpenGL ES: A cross-platform graphics API used for rendering 2D and 3D graphics efficiently.
- WebKit: A web rendering engine used to display web content inside Android applications.
- Media Libraries: Provide support for audio and video playback, recording, and streaming of multimedia content.
These libraries are used by the Android Framework and applications.
5. Hardware Abstraction Layer (HAL)
The Hardware Abstraction Layer (HAL) provides a standard interface between hardware and the Android system. Its main purpose is:
- Hides hardware implementation details from higher layers.
- Allows Android to work on different devices without changing application code.
- Examples of hardware handled by HAL are: Camera, Bluetooth, Sensors, GPS
6. Linux Kernel
Android was created on the open-source kernel of Linux. One main reason for choosing this kernel was that it provided proven core features on which to develop the Android operating system. The features of the Linux kernel are:
- Security: Linux kernel handles the security between the application and the system.
- Memory Management: It efficiently handles memory management thereby providing the freedom to develop our apps.
- Process Management: It manages the process well and allocates resources to processes whenever they need them.
- Network Stack: It effectively handles network communication.
- Driver Model: It ensures that the application works. Hardware manufacturers can build their drivers into the Linux build.
7. Libraries
Running on top of the kernel, the Android framework was developed with various features. It consists of various C/C++ core libraries with numerous open-source tools. Some of these are:
- Android Runtime: The Android runtime consists of core libraries of Java and ART(the Android RunTime). Older versions of Android (4.x and earlier) had Dalvik runtime.
- Open GL(graphics library): This cross-language, cross-platform application program interface (API) is used to produce 2D and 3D computer graphics.
- WebKit: This open-source web browser engine provides all the functionality to display web content and simplify page loading.
- Media frameworks: These libraries allow you to play and record audio and video.
- Secure Socket Layer (SSL): These libraries are there for Internet security.