From 9066cfe9886ac131c34d59ed0e2d287b0e3c0087 Mon Sep 17 00:00:00 2001
From: The Android Open Source Project <initial-contribution@android.com>
Date: Tue, 3 Mar 2009 19:31:44 -0800
Subject: auto import from //depot/cupcake/@135843

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+page.title=What is Android?
+@jd:body
+
+<p>Android is a software stack for mobile devices that includes an operating
+system, middleware and key applications. The <a
+href="http://code.google.com/android/download.html">Android SDK</a>
+provides the tools and APIs necessary to begin developing applications on the
+Android platform using the Java programming language.</p>
+
+<h2>Features</h2>
+
+<ul>
+    <li><strong>Application framework</strong> enabling reuse and replacement
+    of components</li>
+    <li><strong>Dalvik virtual machine</strong> optimized for mobile
+        devices</li>
+    <li><strong>Integrated browser</strong> based on the open source <a
+    href="http://webkit.org/">WebKit</a> engine </li>
+    <li><strong>Optimized graphics</strong> powered by a custom 2D graphics library; 3D
+    graphics based on the OpenGL ES 1.0 specification (hardware acceleration
+    optional)</li>
+    <li><strong>SQLite</strong> for structured data storage</li>
+    <li><strong>Media support</strong> for common audio, video, and still
+    image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG,
+    GIF)</li>
+    <li><strong>GSM Telephony</strong> (hardware dependent)</li>
+    <li><strong>Bluetooth, EDGE, 3G, and WiFi</strong> (hardware dependent)</li>
+    <li><strong>Camera, GPS, compass, and accelerometer</strong> (hardware dependent)</li>
+    <li><strong>Rich development environment</strong> including a device
+    emulator, tools for debugging, memory and performance profiling, and a plugin for the Eclipse IDE</li>
+</ul>
+
+<a name="os_architecture" id="os_architecture"></a>
+<h2>Android Architecture</h2> 
+
+<p>The following diagram shows the major components of the Android operating
+system. Each section is described in more detail below.</p>
+
+<p><img src="{@docRoot}images/system-architecture.jpg" alt="Android System Architecture" width="713" height="512"></p>
+
+<a name="applications" id="applications"></a>
+<h2>Applications</h2>
+
+<p>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.</p>
+
+<a name="application_framework" id="application_framework"></a>
+<h2>Application Framework</h2>
+
+<p>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.</p>
+
+<p>Underlying all applications is a set of services and systems, including:
+<ul>
+    <li>A rich and extensible set of <a
+    href="{@docRoot}guide/tutorials/views/index.html">Views</a> that can be used to
+    build an application, including lists, grids, text boxes, buttons, and even
+    an embeddable web browser</li>
+    <li><a href="{@docRoot}guide/topics/providers/content-providers.html">Content
+    Providers</a> that enable applications to access data from other
+    applications (such as Contacts), or to share their own data</li> <li>A <a
+    href="{@docRoot}guide/topics/resources/resources-i18n.html">Resource
+    Manager</a>, providing access to non-code resources such as localized
+    strings, graphics, and layout files</li>
+    <li>A {@link android.app.NotificationManager Notification Manager} that enables
+    all applications to display custom alerts in the status bar</li>
+    <li>An {@link android.app.Activity Activity Manager} that manages the
+    lifecycle of applications and provides a common navigation backstack</li>
+</ul>
+
+<p>For more details and a walkthrough of an application, see the <a
+href="{@docRoot}guide/tutorials/notepad/index.html">Notepad Tutorial</a>.</p>
+    
+<a name="libraries" id="libraries"></a>
+<h2>Libraries</h2>
+
+<p>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:</p>
+<ul>
+    <li><strong>System C library</strong> - a BSD-derived implementation of
+    the standard C system library (libc), tuned for embedded Linux-based
+    devices</li>
+    <li><strong>Media Libraries</strong> - 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</li>
+    <li><strong>Surface Manager</strong> - manages access to the display
+    subsystem and seamlessly composites 2D and 3D graphic layers from multiple
+    applications</li>
+    <li><strong>LibWebCore</strong> - a modern web browser engine which
+    powers both the Android browser and an embeddable web view</li>
+    <li><strong>SGL</strong> - the underlying 2D graphics
+    engine</li>
+    <li><strong>3D libraries</strong> - 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</li>
+    <li><strong>FreeType</strong> - bitmap and vector font rendering</li>
+    <li><strong>SQLite</strong> - a powerful and lightweight relational
+    database engine available to all applications</li>
+</ul>
+
+<a name="runtime" id="runtime"></a>
+
+<h2>Android Runtime</h2>
+
+<p>Android includes a set of core libraries that provides most of
+the functionality available in the core libraries of the Java programming
+language.</p>
+
+<p>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 &quot;dx&quot; tool.</p>
+
+<p>The Dalvik VM relies on the Linux kernel for underlying functionality such
+as threading and low-level memory management.</p>
+
+<a name="kernel" id="kernel"></a>
+
+<h2>Linux Kernel</h2>
+
+<p>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.</p>
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