What is Android?

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

所谓的Andriod就是An Open Handset Alliance Project（开放手机联盟，广为人知的“山寨”即得益于此），从Google力推的Andriod可以看出Google想要攻占移动数据市场的全球战略的野心，而我们每个人都将会得益于此~

下面是Andriod的架构简介。

Features

Application frameworkenabling reuse and replacement of components
Dalvik virtual machineoptimized for mobile devices
Integrated browserbased on the open sourceWebKitengine
Optimized graphicspowered by a custom 2D graphics library; 3D graphics based on the OpenGL ES 1.0 specification (hardware acceleration optional)
SQLitefor structured data storage
Media supportfor 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 environmentincluding 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.

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.

Application Framework

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 ofViewsthat can be used to build an application, including lists, grids, text boxes, buttons, and even an embeddable web browser
Content Providersthat enable applications to access data from other applications (such as Contacts), or to share their own data
AResource Manager, providing access to non-code resources such as localized strings, graphics, and layout files
ANotification Managerthat enables all applications to display custom alerts in the status bar
AnActivity Managerthat manages the life cycle of applications and provides a common navigation backstack

For more details and a walkthrough of an application, seeWriting an Android Application.

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:

System C library- a BSD-derived implementation of the standard C system library (libc), tuned for embedded Linux-based devices
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
Surface Manager- manages access to the display subsystem and seamlessly composites 2D and 3D graphic layers from multiple applications
LibWebCore- a modern web browser engine which powers both the Android browser and an embeddable web view
SGL- the underlying 2D graphics engine
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
FreeType- bitmap and vector font rendering
SQLite- a powerful and lightweight relational database engine available to all applications

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.

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.

来自于code.google.com

基于Linux内核的Andriod会带给我们什么？我好像看到了Windows平台在个人平台上的统治力的再现，不过这次是Google，这次主人是大家，而非像MS一样的独裁者。希望Google主导的Andriod平台能在个人移动平台上取得成功，毕竟Andriod已经将Map作为它的一个基本的应用，这一点值得每一个GISer欣慰~~

有了塞班、Linux和WM，现在又有了Andriod（虽然基于Linux平台），我们应该期待的是让暴风雨来的更猛烈些吧！