What is android?

Android is a software stack for mobile devices that includes an operating system, middleware and key applications. The Android SDK provides the tools and APIs necessary to begin developing applications on the Android platform using the Java programming language.
Features

* Application framework enabling reuse and replacement of components
* Dalvik virtual machine optimized for mobile devices
* Integrated browser based on the open source WebKit engine
* Optimized graphics powered by a custom 2D graphics library; 3D graphics based on the OpenGL ES 1.0 specification (hardware acceleration optional)
* SQLite for structured data storage
* Media support for common audio, video, and still image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)
* GSM Telephony (hardware dependent)
* Bluetooth, EDGE, 3G, and WiFi (hardware dependent)
* Camera, GPS, compass, and accelerometer (hardware dependent)
* Rich development environment including a device emulator, tools for debugging, memory and performance profiling, and a plugin for the Eclipse IDE

Android Architecture

The following diagram shows the major components of the Android operating system. Each section is described in more detail below.

Android System Architecture