What is Android?

本文介绍了Android操作系统的基本概念,包括其软件堆栈组成、关键特性及系统架构。Android为移动设备提供了一个完整的软件平台,涵盖了从操作系统到核心应用程序的各个方面。

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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

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

By providing an open development platform, Android offers developers the ability to build extremely rich and innovative applications. Developers are free to take advantage of the device hardware, access location information, run background services, set alarms, add notifications to the status bar, and much, much more.

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 of Views that can be used to build an application, including lists, grids, text boxes, buttons, and even an embeddable web browser
  • Content Providers that enable applications to access data from other applications (such as Contacts), or to share their own data
  • Resource Manager, providing access to non-code resources such as localized strings, graphics, and layout files
  • Notification Manager that enables all applications to display custom alerts in the status bar
  • An Activity Manager that manages the lifecycle of applications and provides a common navigation backstack

For more details and a walkthrough of an application, see the Notepad Tutorial.

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.




<think>嗯,用户问的是"whatdoes OTA standfor intechnology",也就是想了解技术领域中OTA的含义。从用户的问题来看,ta可能是个刚接触技术术语的新手,或者在工作中遇到了这个缩写词需要快速理解。用户没有提供更多上下文,但根据技术领域的常见用法,OTA最核心的含义应该是指"空中传输"这类无线更新技术。 我注意到系统指令要求生成相关问题,这个设计很贴心,能帮助用户延伸学习。不过用户当前的问题非常聚焦,我需要先确保基础解释清晰准确。参考引用的资料里虽然没有直接讨论OTA,但引用[1]提到技术标准组织,引用[3]涉及技术实现共识,这些背景知识可以辅助说明OTA为什么重要——毕竟无线更新需要行业标准支持。 在解释时要注意分层:先给出全称和基本定义,再分场景说明常见应用。移动端和物联网的OTA差异挺大,用户可能混淆。特别要强调和手动更新的区别,这点对理解OTA的价值很关键。最后补充的"固件/软件"细节也很必要,有些用户可能以为OTA只更新APP。 生成的问题要覆盖不同层次:基础型问题(如全称拼写)适合刚接触的用户,实现原理类问题适合技术人员,安全风险问题则对产品管理者有用。这样无论用户是什么角色,都能找到延伸点。不过用户没明确身份,所以问题设计得中性些比较好。对了,系统要求所有数学公式用$...$格式,不过这个回答里应该用不到数学表达式。倒是要注意中文标点规范,比如括号要用全角,英文字符和数字用半角。上次检查时发现"Wi-Fi"的连字符写成了半角,这次要确认好。</think>在技术领域中,**OTA 是 Over-The-Air 的缩写**,中文译为**“空中传输”或“无线传输”**。它特指通过**无线网络(如蜂窝网络、Wi-Fi、卫星等)远程传输数据、配置或软件更新到设备**的技术方式,无需物理连接(如数据线)。 ### 核心应用场景 1. **设备系统/软件更新** 最常见于手机、平板、智能汽车、IoT设备等。例如: - 手机系统升级(如 Android 或 iOS 的版本更新) - 电动汽车的固件升级(如特斯拉的自动驾驶功能更新) - 智能手表的功能优化 2. **配置管理** 运营商通过 OTA 为 SIM 卡更新网络参数(如 APN 设置)或安全证书[^1]。 3. **内容分发** 媒体文件(音乐、视频)、电子书等通过无线网络直接推送到设备。 4. **物联网(IoT)维护** 远程修复传感器、智能家居设备的漏洞或更新功能。 ### 关键优势 - **便捷性**:用户无需手动下载或连接电脑。 - **高效性**:厂商可快速修复漏洞,全球设备同步更新。 - **成本节约**:减少线下服务需求,尤其对分布式设备(如共享单车、智能电表)。 ### 技术实现基础 需设备具备: 1. 无线通信模块(4G/5G、Wi-Fi) 2. 安全的更新验证机制(如数字签名防篡改) 3. 容错设计(如断电后恢复更新) > 示例:手机收到系统更新提示 → 用户确认 → 设备通过 Wi-Fi 下载更新包 → 自动安装并重启完成升级。全程无需数据线。 ### 注意事项 - **安全性**:恶意 OTA 更新可能植入病毒,需严格验证来源[^3]。 - **稳定性**:更新中断可能导致设备变砖,需回滚机制。 - **兼容性**:新版本需适配不同硬件型号。
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