Android Architecture

Android Architecture 

1. Applications: basic applications include an email client, SMS program, calendar, maps, browser, contacts, and others. All applications are written in Java programming language. 

2. Application Framework: the developers have full access to the same framework APIs used by applications base. The architecture is designed to simplify the reuse of components, any application can publish its capabilities and any other application can then make use of those capabilities (subject to safety rules framework). This same mechanism allows components to be replaced by the user. 

3. Libraries: Android includes a set of libraries C / C + + used by various components of the Android system. These features are exposed to developers through the Android application framework, some of them: System C library (C standard library implementation), media libraries, graphics libraries, 3d, SQLite, and others. 

4. Runtime Android: Android includes a set of base libraries that provide most of the features available in the libraries of the Java language base. Every Android application runs 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. Dalvik executes files in the Dalvik Executable (. Dex), which is optimized for minimum memory. The virtual machine is based on records, and runs classes compiled by the Java compiler that have been transformed by the tool to formato.dex included “dx”.

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

Dalvik Virtual Machine

The Dalvik virtual machine is a register-based virtual machine, designed and written by Dan Bornstein with contributions from other Google engineers as part of the Android mobile phone platform.
It is optimized for low memory requirements, and is designed to allow multiple VM instances to run at once, relying on the underlying operating system for process isolation, memory management and threading support. Dalvik is often referred to as a Java Virtual Machine, but this is not strictly accurate, as the bytecode on which it operates is not Java bytecode. Instead, a tool named dx, included in the Android SDK, transforms the Java Class files of Java classes compiled by a regular Java compiler into another class file format (the .dex format).