<span id="overview"></span><h1 id="technical-overview"><span id="overview"></span>Technical Overview</h1>
<div class="contents local" id="contents" style="display: none">
<ul class="small-gap">
-<li><a class="reference internal" href="#introduction" id="id2">Introduction</a></li>
-<li><a class="reference internal" href="#why-use-native-client" id="id3">Why use Native Client?</a></li>
-<li><a class="reference internal" href="#common-use-cases" id="id4">Common use cases</a></li>
-<li><p class="first"><a class="reference internal" href="#how-native-client-works" id="id5">How Native Client works</a></p>
+<li><a class="reference internal" href="#why-use-native-client" id="id7">Why use Native Client?</a></li>
+<li><a class="reference internal" href="#benefits-of-native-client" id="id8">Benefits of Native Client</a></li>
+<li><a class="reference internal" href="#common-use-cases" id="id9">Common use cases</a></li>
+<li><p class="first"><a class="reference internal" href="#how-native-client-works" id="id10">How Native Client works</a></p>
<ul class="small-gap">
-<li><a class="reference internal" href="#security" id="id6">Security</a></li>
-<li><a class="reference internal" href="#portability" id="id7">Portability</a></li>
-<li><a class="reference internal" href="#toolchains" id="id8">Toolchains</a></li>
+<li><a class="reference internal" href="#toolchains" id="id11">Toolchains</a></li>
+<li><a class="reference internal" href="#security" id="id12">Security</a></li>
+<li><a class="reference internal" href="#portability" id="id13">Portability</a></li>
</ul>
</li>
-<li><p class="first"><a class="reference internal" href="#native-client-in-a-web-application" id="id9">Native Client in a web application</a></p>
+<li><p class="first"><a class="reference internal" href="#structure-of-a-web-application" id="id14">Structure of a web application</a></p>
<ul class="small-gap">
-<li><a class="reference internal" href="#pepper-plugin-api" id="id10">Pepper Plugin API</a></li>
+<li><a class="reference internal" href="#pepper-plug-in-api" id="id15">Pepper plug-in API</a></li>
</ul>
</li>
-<li><a class="reference internal" href="#versioning" id="id11">Versioning</a></li>
-<li><a class="reference internal" href="#where-to-start" id="id12">Where to start</a></li>
+<li><a class="reference internal" href="#where-to-start" id="id16">Where to start</a></li>
</ul>
-</div><h2 id="introduction">Introduction</h2>
-<p><strong>Native Client</strong> (NaCl) is an open-source technology for running native
+</div><p><strong>Native Client</strong> (NaCl) is an open-source technology for running native
compiled code in the browser, with the goal of maintaining the portability
and safety that users expect from web applications. Native Client expands web
-programming beyond JavaScript, enabling developers to enhance their web
-applications using their preferred language. This document describes some of
-the key benefits and common use cases of Native Client.</p>
+programming beyond JavaScript, enabling you to enhance your web applications
+using your preferred language. This document describes some of the key benefits
+and common use cases of Native Client.</p>
<p>Google has implemented the open-source <a class="reference external" href="http://www.chromium.org/nativeclient">Native Client project</a> in the Chrome browser on Windows, Mac,
-Linux, and Chrome OS. The <a class="reference internal" href="/native-client/sdk/download.html"><em>Native Client Software Development Kit (SDK)</em></a>, itself an open-source project, lets developers create web
-applications that use NaCl and run in Chrome across multiple platforms.</p>
-<p>A web application that uses Native Client generally consists of a combination of
-JavaScript, HTML, CSS, and a NaCl module that is written in a language supported
-by the SDK. The NaCl SDK currently supports C and C++; as compilers for
-additional languages are developed, the SDK will be updated to support those
-languages as well.</p>
-<img alt="/native-client/images/web-app-with-nacl.png" src="/native-client/images/web-app-with-nacl.png" />
-<h2 id="why-use-native-client">Why use Native Client?</h2>
+Linux, and Chrome OS. The <a class="reference internal" href="/native-client/sdk/download.html"><em>Native Client Software Development Kit (SDK)</em></a>, itself an open-source project, lets you create web applications
+that use NaCl and run in Chrome across multiple platforms.</p>
+<p>A Native Client web application consists of JavaScript, HTML, CSS, and a NaCl
+module written in a language supported by the SDK. The NaCl SDK currently
+supports C and C++; as compilers for additional languages are developed, the SDK
+will be updated.</p>
+<div class="figure">
+<img alt="A web application with and without Native Client" src="/native-client/images/web-app-with-nacl.png" />
+<p class="caption">A web application with and without Native Client</p>
+</div>
+<p>Native Client comes in two flavors: traditional (NaCl) and portable (PNaCl).
+Traditional, which must be distributed through the Chrome Web Store lets you
+target a specific hardware platform. Portable can run on the open web. A
+bitcode file that can be loaded from any web server is downloaded to a client
+machine and converted to hardware-specific code before any execution. For
+details, see <a class="reference internal" href="/native-client/nacl-and-pnacl.html"><em>NaCl and PNaCl</em></a>.</p>
+<h2 id="why-use-native-client"><span id="id1"></span>Why use Native Client?</h2>
<p>Native Client open-source technology is designed to run compiled code
-securely inside a browser at near-native speeds. Native Client puts web
-applications on the same playing field as traditional (locally-run)
-software—it provides the means to fully harness the client’s computational
-resources for applications such as 3D games, multimedia editors, CAD modeling,
-client-side data analytics, and interactive simulations.
-Native Client also aims to give C and C++ (and eventually other languages) the
-same level of portability and safety that JavaScript provides on the web today.</p>
-<p>Here are a few of the key benefits that Native Client offers:</p>
+securely inside a browser at near-native speeds. Native Client gives web
+applications some advantages of desktop software. Specifically, it provides the
+means to fully harness the client’s computational resources for applications
+such as:</p>
<ul class="small-gap">
-<li><strong>Graphics, audio, and much more:</strong> Run native code modules that render 2D
+<li>3D games</li>
+<li>multimedia editors</li>
+<li>CAD modeling</li>
+<li>client-side data analytics</li>
+<li>interactive simulations.</li>
+</ul>
+<p>Native Client gives C and C++ (and other languages targeting it) the same level
+of portability and safety as JavaScript.</p>
+<h2 id="benefits-of-native-client"><span id="id2"></span>Benefits of Native Client</h2>
+<p>Benefits of Native Client include:</p>
+<ul class="small-gap">
+<li><strong>Graphics, audio, and much more:</strong> Running native code modules that render 2D
and 3D graphics, play audio, respond to mouse and keyboard events, run on
-multiple threads, and access memory directly—all without requiring
-the user to install a plugin.</li>
-<li><strong>Portability:</strong> Write your applications once and you’ll be able to run them
-across operating systems (Windows, Linux, Mac, and Chrome OS) and CPU
-architectures (x86 and ARM).</li>
-<li><strong>Easy migration path to the web:</strong> Many developers and companies have years
-of work invested in existing desktop applications. Native Client makes the
-transition from the desktop to a web application significantly easier because
-it supports C and C++.</li>
-<li><strong>Security:</strong> Native Client uses a double sandbox model designed to protect
-the user’s system from malicious or buggy applications. This model offers the
-safety of traditional web applications without sacrificing performance and
-without requiring users to install a plugin.</li>
-<li><strong>Performance:</strong> Native Client allows web applications to run at speeds
-comparable to desktop applications (within 5-15% of native speed).
-Native Client also allows applications to harness all available CPU cores via
-a threading API; this enables demanding applications such as console-quality
-games to run inside the browser.</li>
+multiple threads, and access memory directly—all without requiring the user
+to install a plug-in.</li>
+<li><strong>Portability:</strong> Writing your applications once and running them on multiple
+operating systems (Windows, Linux, Mac, and Chrome OS) and CPU architectures
+(x86 and ARM).</li>
+<li><strong>Easy migration path to the web:</strong> Leveraging years of work in existing
+desktop applications. Native Client makes the transition from the desktop to
+a web application significantly easier because it supports C and C++.</li>
+<li><strong>Security:</strong> Protecting the user’s system from malicious or buggy
+applications through Native Client’s double sandbox model. This model offers
+the safety of traditional web applications without sacrificing performance
+and without requiring users to install a plug-in.</li>
+<li><strong>Performance:</strong> Running at speeds within 5% to 15% of a native desktop
+application. Native Client also allows applications to harness all available
+CPU cores via a threading API. This enables demanding applications such as
+console-quality games to run inside the browser.</li>
</ul>
-<h2 id="common-use-cases">Common use cases</h2>
+<h2 id="common-use-cases"><span id="id3"></span>Common use cases</h2>
<p>Typical use cases for Native Client include the following:</p>
<ul class="small-gap">
-<li><strong>Existing software components:</strong> With support for C and C++, Native
-Client enables you to reuse existing software modules in
-web applications—you don’t need to rewrite and debug code
-that’s already proven to work well.</li>
+<li><strong>Existing software components:</strong> Native Client lets you repurpose existing
+C and C++ software in web applications. You don’t need to rewrite and debug
+code that already works. It also lets your application take advantage of
+things the browser does well such as handling user interaction and processing
+events. You can also take advantage of the latest developments in HTML5.</li>
<li><strong>Legacy desktop applications:</strong> Native Client provides a smooth migration
path from desktop applications to the web. You can port and recompile existing
code for the computation engine of your application directly to Native Client,
-and need repurpose only the user interface and event handling portions to the
-new browser platform. Native Client allows you to embed existing functionality
-directly into the browser. At the same time, your application can take
-advantage of things the browser does well: handling user interaction and
-processing events, based on the latest developments in HTML5.</li>
+and need rebuild only the user interface and event handling portions for the
+browser.</li>
<li><strong>Heavy computation in enterprise applications:</strong> Native Client can handle the
number crunching required by large-scale enterprise applications. To ensure
-protection of user data, Native Client enables you to build complex
-cryptographic algorithms directly into the browser so that unencrypted data
-never goes out over the network.</li>
+protection of user data, Native Client lets you run complex cryptographic
+algorithms directly in the browser so that unencrypted data never goes out
+over the network.</li>
<li><strong>Multimedia applications:</strong> Codecs for processing sounds, images, and movies
can be added to the browser in a Native Client module.</li>
<li><strong>Games:</strong> Native Client lets web applications run at close to native
artificial intelligence module that powers a sophisticated web game.
Native Client also enables applications to run unchanged across
many platforms.</li>
-<li><strong>Any application that requires acceleration</strong>: Native Client fits seamlessly
-into web applications—it’s up to you to decide to what extent to use it.
+<li><strong>Any application that requires acceleration:</strong> Native Client fits seamlessly
+into web applications. It’s up to you to decide to what extent to use it.
Use of Native Client covers the full spectrum from complete applications to
-small optimized routines that accelerate vital parts of web apps.</li>
+small optimized routines that accelerate vital parts of web applications.</li>
</ul>
<h2 id="how-native-client-works"><span id="link-how-nacl-works"></span>How Native Client works</h2>
-<p>Native Client is an umbrella name for a set of interrelated software components
-that work together to provide a way to develop C/C++ applications and run them
-securely on the web.</p>
-<p>At a high level, Native Client consists of:</p>
+<p>Native Client is an umbrella name for a set of related software components for
+developing C/C++ applications and running them securely on the web. At a high
+level, Native Client consists of:</p>
<ul class="small-gap">
-<li><strong>Toolchains</strong>: collections of development tools (compilers, linkers, etc.)
-that transform C/C++ code to Native Client modules.</li>
-<li><strong>Runtime components</strong>: components embedded in the browser or other
-host platforms that allow execution of Native Client modules
-securely and efficiently.</li>
+<li><strong>Toolchains:</strong> collections of development tools (compilers, linkers, etc.)
+that transform C/C++ code to Portable Native Client modules or Native Client
+modules.</li>
+<li><strong>Runtime components:</strong> components embedded in the browser or other host
+platforms that allow execution of Native Client modules securely and
+efficiently.</li>
</ul>
<p>The following diagram shows how these components interact:</p>
-<img alt="/native-client/images/nacl-pnacl-component-diagram.png" src="/native-client/images/nacl-pnacl-component-diagram.png" />
-<p>The left side of the diagram shows how to use Portable Native Client
-(PNaCl, pronounced “pinnacle”). Developers use the PNaCl toolchain
-to produce a single, portable (<strong>pexe</strong>) module. At runtime, a translator
-built into the browser translates the pexe into native code for the
-relevant client architecture.</p>
-<p>The right side of the diagram shows how to use traditional (non-portable)
-Native Client. Developers use a nacl-gcc based toolchain to produce multiple
-architecture-dependent (<strong>nexe</strong>) modules, which are packaged into an
-application. At runtime, the browser decides which nexe to load based
-on the architecture of the client machine.</p>
-<h3 id="security">Security</h3>
+<div class="figure">
+<img alt="The Native Client toolchains and their outputs" src="/native-client/images/nacl-pnacl-component-diagram.png" />
+<p class="caption">The Native Client toolchains and their outputs</p>
+</div>
+<h3 id="toolchains"><span id="id4"></span>Toolchains</h3>
+<p>A Native Client toolchain consists of a compiler, a linker, an assembler and
+other tools that are used to convert C/C++ source code into a module that is
+loadable by a browser.</p>
+<p>The Native Client SDK provides two toolchains:</p>
+<ul class="small-gap">
+<li>The left side of the diagram shows <strong>Portable Native Client</strong> (PNaCl,
+pronounced “pinnacle”). An LLVM based toolchain produces a single, portable
+(<strong>pexe</strong>) module. At runtime an ahead-of-time (AOT) translator, built into
+the browser, translates the pexe into native code for the relevant client
+architecture.</li>
+<li>The right side of the diagram shows <strong>(non-portable) Native Client</strong>. A GCC
+based toolchain produces multiple architecture-dependent (<strong>nexe</strong>) modules,
+which are packaged into an application. At runtime the browser determines
+which nexe to load based on the architecture of the client machine.</li>
+</ul>
+<p>The PNaCl toolchain is recommended for most applications. The NaCl-GCC
+toolchain should only be used for applications that won’t be distributed on the
+open web.</p>
+<h3 id="security"><span id="id5"></span>Security</h3>
<p>Since Native Client permits the execution of native code on client machines,
special security measures have to be implemented:</p>
<ul class="small-gap">
<li>The NaCl sandbox ensures that code accesses system resources only through
-safe, whitelisted APIs, and operates within its limits without attempting to
+safe, whitelisted APIs, and operates within its limits without attempting to
interfere with other code running either within the browser or outside it.</li>
-<li>The NaCl validator statically analyzes code prior to running it
-to make sure it only uses code and data patterns that are permitted and safe.</li>
+<li>The NaCl validator statically analyzes code before running it to make sure it
+only uses code and data patterns that are permitted and safe.</li>
</ul>
-<p>The above security measures are in addition to the existing sandbox in the
-Chrome browser—the Native Client module always executes in a process with
+<p>These security measures are in addition to the existing sandbox in the
+Chrome browser. The Native Client module always executes in a process with
restricted permissions. The only interaction between this process and the
-outside world is through sanctioned browser interfaces. Because of the
+outside world is through defined browser interfaces. Because of the
combination of the NaCl sandbox and the Chrome sandbox, we say that
-Native Client employs a double sandbox design.</p>
-<h3 id="portability">Portability</h3>
+Native Client employs a <strong>double sandbox</strong> design.</p>
+<h3 id="portability"><span id="id6"></span>Portability</h3>
<p>Portable Native Client (PNaCl, prounounced “pinnacle”) employs state-of-the-art
compiler technology to compile C/C++ source code to a portable bitcode
executable (<strong>pexe</strong>). PNaCl bitcode is an OS- and architecture-independent
applications</em></a>.</p>
<p>The PNaCl translator is a component embedded in the Chrome browser; its task is
to run pexe modules. Internally, the translator compiles a pexe to a nexe
-(a native executable for the client platform’s architecture), and then executes
-the nexe within the Native Client sandbox as described above. It also uses
-intelligent caching to avoid re-compiling the pexe if it was previously compiled
-on the client’s browser.</p>
+(described above), and then executes the nexe within the Native Client sandbox
+as described above. The translator uses intelligent caching to avoid
+re-compiling the pexe if it was previously compiled on the client’s browser.</p>
<p>Native Client also supports the execution of nexe modules directly in the
-browser. However, since nexes contain architecture-specific machine code,
-they are not allowed to be distributed on the open web—they can only be
-used as part of applications and extensions that are installed from the
-Chrome Web Store.</p>
+browser. However, since nexes contain architecture-specific machine code, they
+are not allowed to be distributed on the open web. They can only be used as part
+of applications and extensions that are installed from the Chrome Web Store.</p>
<p>For more details on the difference between NaCl and PNaCl, see
<a class="reference internal" href="/native-client/nacl-and-pnacl.html"><em>NaCl and PNaCl</em></a>.</p>
-<h3 id="toolchains"><span id="id1"></span>Toolchains</h3>
-<p>A toolchain is a set of tools used to create an application from a set of
-source files. In the case of Native Client, a toolchain consists of a compiler,
-linker, assembler and other tools that are used to convert an
-application written in C/C++ into a module that is loadable by the browser.</p>
-<p>The Native Client SDK provides two toolchains:</p>
-<ul class="small-gap">
-<li>a <strong>PNaCl toolchain</strong> for generating portable NaCl modules (pexe files)</li>
-<li>a <strong>gcc-based toolchain (nacl-gcc)</strong> for generating non-portable NaCl modules
-(nexe files)</li>
-</ul>
-<p>The PNaCl toolchain is recommended for most applications. The nacl-gcc
-toolchain should only be used for applications that will not be distributed
-on the open web.</p>
-<h2 id="native-client-in-a-web-application"><span id="link-nacl-in-web-apps"></span>Native Client in a web application</h2>
+<h2 id="structure-of-a-web-application"><span id="link-nacl-in-web-apps"></span>Structure of a web application</h2>
<p id="application-files">A Native Client application consists of a set of files:</p>
<ul class="small-gap">
-<li><strong>HTML</strong>, <strong>CSS</strong>, and <strong>JavaScript</strong> files, as in any modern web
-application. The JavaScript code is responsible for communicating with the
-NaCl module.</li>
-<li>A <strong>pexe</strong> (portable NaCl) file. This module uses the <a class="reference internal" href="#link-pepper"><em>Pepper</em></a> API, which provides the bridge to JavaScript and
-browser resources.</li>
-<li>A Native Client <strong>manifest</strong> file that specifies the pexe to load, along with
-some loading options. This manifest file is embedded into the HTML page
-through an <code><embed></code> tag, as shown in the figure below.</li>
+<li><p class="first"><strong>HTML and CSS:</strong> The HTML file tells the browser where to find the manifest
+(nmf file) through the embed tag.</p>
+<pre class="prettyprint">
+<embed name="mygame" src="mygame.nmf" type="application/x-pnacl" />
+</pre>
+</li>
+<li><p class="first"><strong>Manifest:</strong> The manifest identifies the module to load and specifies
+options. For example, “mygame.nmf” might look like this:</p>
+<pre class="prettyprint">
+{...
+ ...
+ "url": "mygame.pexe",
+}
+</pre>
+</li>
+<li><strong>pexe (portable NaCl file):</strong> A compiled Native Client module. It uses the
+<a class="reference internal" href="#link-pepper"><em>Pepper API</em></a>, which provides a bridge to JavaScript and
+other browser resources.</li>
</ul>
-<img alt="/native-client/images/nacl-in-a-web-app.png" src="/native-client/images/nacl-in-a-web-app.png" />
+<div class="figure">
+<img alt="Structure of a web application" src="/native-client/images/nacl-in-a-web-app.png" />
+<p class="caption">Structure of a web application</p>
+</div>
<p>For more details, see <a class="reference internal" href="/native-client/devguide/coding/application-structure.html"><em>Application Structure</em></a>.</p>
-<h3 id="pepper-plugin-api"><span id="link-pepper"></span>Pepper Plugin API</h3>
-<p>The Pepper Plugin API (PPAPI), called <strong>Pepper</strong> for convenience, is an
-open-source, cross-platform C/C++ API for web browser plugins. From the point
-of view of Native Client, Pepper allows a C/C++ module to communicate with
-the hosting browser and get access to system-level functions in a safe and
-portable way. One of the security constraints in Native Client is that modules
-cannot make any OS-level calls directly. Pepper provides analogous APIs that
-modules can target instead.</p>
+<h3 id="pepper-plug-in-api"><span id="link-pepper"></span>Pepper plug-in API</h3>
+<p>The Pepper plug-in API (PPAPI), called <strong>Pepper</strong> for convenience, is an
+open-source, cross-platform C/C++ API for web browser plug-ins. Pepper allows a
+C/C++ module to communicate with the hosting browser and to access system-level
+functions in a safe and portable way. One of the security constraints in Native
+Client is that modules cannot make OS-level calls. Pepper provides analogous
+APIs that modules can use instead.</p>
<p>You can use the Pepper APIs to gain access to the full array of browser
capabilities, including:</p>
<ul class="small-gap">
<li><a class="reference internal" href="/native-client/devguide/coding/audio.html"><em>Playing audio</em></a>.</li>
<li><a class="reference internal" href="/native-client/devguide/coding/3D-graphics.html"><em>Rendering 3D graphics</em></a>.</li>
</ul>
-<p>Pepper includes both a C API and a C++ API. The C++ API is a set of bindings
-written on top of the C API. For additional information about Pepper, see
-<a class="reference external" href="http://code.google.com/p/ppapi/wiki/Concepts">Pepper Concepts</a>.</p>
-<h2 id="versioning">Versioning</h2>
-<p>Chrome is released on a six week cycle, and developer versions of Chrome are
-pushed to the public beta channel three weeks before each release. As with any
-software, each release of Chrome may include changes to Native Client and the
-Pepper interfaces that may require modification to existing applications.
-However, modules compiled for one version of Pepper/Chrome should work with
-subsequent versions of Pepper/Chrome. The SDK includes multiple versions of the
-Pepper APIs to help developers make adjustments to API changes and take
-advantage of new features: <a class="reference external" href="/native-client/pepper_stable">stable</a>, <a class="reference external" href="/native-client/pepper_beta">beta</a> and <a class="reference external" href="/native-client/pepper_dev">dev</a>.</p>
+<p>Pepper includes both a <a class="reference internal" href="/native-client/c-api.html"><em>C API</em></a> and a <a class="reference internal" href="/native-client/cpp-api.html"><em>C++ API</em></a>.
+The C++ API is a set of bindings written on top of the C API. For additional
+information about Pepper, see <a class="reference external" href="http://code.google.com/p/ppapi/wiki/Concepts">Pepper Concepts</a>.</p>
<h2 id="where-to-start">Where to start</h2>
<p>The <a class="reference internal" href="/native-client/quick-start.html"><em>Quick Start</em></a> document provides links to downloads and
-documentation that should help you get started with developing and distributing
-Native Client applications.</p>
+documentation to help you get started with developing and distributing Native
+Client applications.</p>
</section>
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