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native_client_sdk/doc_generated/nacl-and-pnacl.html

Index: native_client_sdk/doc_generated/nacl-and-pnacl.html
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 <strong>Portable Native Client</strong>, and provides recommendations for when to use each.</p>
 <div class="contents local" id="contents" style="display: none">
 <ul class="small-gap">
-<li><a class="reference internal" href="#native-client-nacl" id="id3">Native Client (NaCl)</a></li>
-<li><a class="reference internal" href="#portable-native-client-pnacl" id="id4">Portable Native Client (PNaCl)</a></li>
-<li><a class="reference internal" href="#when-to-use-pnacl" id="id5">When to use PNaCl</a></li>
-<li><a class="reference internal" href="#when-to-use-nacl" id="id6">When to use NaCl</a></li>
+<li><a class="reference internal" href="#native-client-nacl" id="id6">Native Client (NaCl)</a></li>
+<li><a class="reference internal" href="#portable-native-client-pnacl" id="id7">Portable Native Client (PNaCl)</a></li>
+<li><a class="reference internal" href="#when-to-use-pnacl" id="id8">When to use PNaCl</a></li>
+<li><a class="reference internal" href="#when-to-use-nacl" id="id9">When to use NaCl</a></li>
 </ul>
 
-</div><h2 id="native-client-nacl">Native Client (NaCl)</h2>
+</div><h2 id="native-client-nacl"><span id="id2"></span>Native Client (NaCl)</h2>
 <p>Native Client enables the execution of native code securely inside web
 applications through the use of advanced <a class="reference external" href="http://research.google.com/pubs/pub35649.html">Software Fault Isolation (SFI)
-techniques</a>.  Since its launch in
-2011, Native Client has provided developers with the ability to harness a
-client machine&#8217;s computational power to a much fuller extent than traditional
-web technologies, by running compiled C and C++ code at near-native speeds and
-taking advantage of multiple cores with shared memory.</p>
-<p>While Native Client provides operating system independence, it requires
-developers to generate architecture-specific executable
-(<strong>nexe</strong>) modules for each hardware platform. This is not only inconvenient
-for developers, but architecture-specific machine code is not portable and thus
-not well-suited for the open web. The traditional method of application
-distribution on the web is through a self-contained bundle of HTML, CSS,
-JavaScript, and other resources (images, etc.) that can be hosted on a server
-and run inside a web browser.  With this type of distribution, a website
-created today should still work years later, on all platforms.
-Architecture-specific executables are clearly not a good fit for distribution
-on the web. As a consequence, Native Client has been restricted to
-applications and browser extensions that are installed through the
+techniques</a>. Native Client
+allows you to harness a client machine&#8217;s computational power to a fuller extent
+than traditional web technologies. It does this by running compiled C and C++
+code at near-native speeds, and exposing a CPU&#8217;s full capabilities, including
+SIMD vectors and multiple-core processing with shared memory.</p>
+<p>While Native Client provides operating system independence, it requires you to
+generate architecture-specific executables (<strong>nexe</strong>) for each hardware
+platform. This is neither portable nor convenient, making it ill-suited for the
+open web.</p>
+<p>The traditional method of application distribution on the web is through self-
+contained bundles of HTML, CSS, JavaScript, and other resources (images, etc.)
+that can be hosted on a server and run inside a web browser. With this type of
+distribution, a website created today should still work years later, on all
+platforms. Architecture-specific executables are clearly not a good fit for
+distribution on the web. Consequently, Native Client has been until recently
+restricted to applications and browser extensions that are installed through the
 Chrome Web Store.</p>
-<h2 id="portable-native-client-pnacl">Portable Native Client (PNaCl)</h2>
+<h2 id="portable-native-client-pnacl"><span id="id3"></span>Portable Native Client (PNaCl)</h2>
 <p>PNaCl solves the portability problem by splitting the compilation process
 into two parts:</p>
 <ol class="arabic simple">
-<li>compiling the source code to a portable bitcode format, and</li>
-<li>translating the bitcode to a host-specific executable just before execution.</li>
+<li>compiling the source code to a bitcode executable (pexe), and</li>
+<li>translating the bitcode to a host-specific executable as soon as the module
+loads in the browser but before any code execution.</li>
 </ol>
-<p>PNaCl enables developers to distribute <strong>portable executables</strong> (<strong>pexe</strong>)
-modules that the hosting environment (in other words, the Chrome browser) can
-translate to native code before executing. This portability aligns Native Client
-with existing open web technologies such as JavaScript. A developer can
-distribute a <strong>pexe</strong> as part of an application (along with HTML, CSS, and
-JavaScript), and the user&#8217;s machine is simply able to run it.</p>
-<p>With PNaCl, a developer generates a single <strong>pexe</strong> from source code,
-rather than multiple platform-specific nexes. The <strong>pexe</strong> provides both
-architecture- and OS-independence. Since the <strong>pexe</strong> uses an abstract,
-architecture-independent format, it does not suffer from the portability
-problem described above. Future versions of hosting environments should
-have no problem executing the <strong>pexe</strong>, even on new architectures.
-Moreover, if an existing architecture is subsequently enhanced, the
-<strong>pexe</strong> doesn&#8217;t even have to be recompiled. In some cases the
-client-side translation will automatically be able to take advantage of
-the new capabilities. A <strong>pexe</strong> module can be part of any web
-application. It does not have to be distributed through the Chrome Web
-Store. In short, PNaCl combines the portability of existing web technologies
-with the performance and security benefits of Native Client.</p>
+<p>This portability aligns Native Client with existing open web technologies such
+as JavaScript. You can distribute a pexe as part of an application (along with
+HTML, CSS, and JavaScript), and the user&#8217;s machine is simply able to run it.</p>
+<p>With PNaCl, you&#8217;ll generate a single pexe, rather than multiple platform-
+specific nexes. Since the pexe uses an abstract, architecture- and OS-
+independent format, it does not suffer from the portability problem described
+above. Although, PNaCl can be more efficient on some operating systems than on
+others. PNaCl boasts the same level of security as NaCl. Future versions of
+hosting environments should have no problem executing the pexe, even on new
+architectures. Moreover, if an existing architecture is enhanced, the pexe
+doesn&#8217;t need to be recompiled. In some cases the client-side translation will
+automatically take advantage of new capabilities. A pexe can be part of any web
+application. It does not have to be distributed through the Chrome Web Store. In
+short, PNaCl combines the portability of existing web technologies with the
+performance and security benefits of Native Client.</p>
 <p>PNaCl is a new technology, and as such it still has a few limitations
 as compared to NaCl. These limitations are described below.</p>
-<h2 id="when-to-use-pnacl">When to use PNaCl</h2>
+<h2 id="when-to-use-pnacl"><span id="id4"></span>When to use PNaCl</h2>
 <p>PNaCl is the preferred toolchain for Native Client, and the only way to deploy
-Native Client modules on the open web. Unless your project is subject to one
-of the narrow limitations described below
-(see <a class="reference internal" href="#when-to-use-nacl"><em>When to use NaCl</em></a>), you should use PNaCl.</p>
-<p>Beginning with version 31, the Chrome browser supports translation of
-<strong>pexe</strong> modules and their use in web applications, without requiring
-any installation (either of a browser plugin or of the applications
-themselves). Native Client and PNaCl are open-source technologies, and
-our hope is that they will be added to other hosting platforms in the
-future.</p>
-<p>If controlled distribution through the Chrome Web Store is an important part
-of your product plan, the benefits of PNaCl are less critical for you. But
-you can still use the PNaCl toolchain and distribute your application
-through the Chrome Web Store, and thereby take advantage of the
-conveniences of PNaCl, such as not having to explicitly compile your application
-for all supported architectures.</p>
-<h2 id="when-to-use-nacl"><span id="id2"></span>When to use NaCl</h2>
-<p>The limitations below apply to the current release of PNaCl. If any of
-these limitations are critical for your application, you should use
-non-portable NaCl:</p>
+Native Client modules without the Google Web Store. Unless your project is
+subject to one of the narrow limitations described under &#8220;<a class="reference internal" href="#when-to-use-nacl"><em>When to use
+NaCl</em></a>&#8221;, you should use PNaCl.</p>
+<p>Since version 31, Chrome supports translation of pexe
+modules and their use in web applications without requiring installation either
+of a browser plug-in or of the applications themselves. Native Client and PNaCl
+are open-source technologies, and our hope is that they will be added to other
+hosting platforms in the future.</p>
+<p>If controlled distribution through the Chrome Web Store is an important part of
+your product plan, the benefits of PNaCl are less critical for you. But you can
+still use the PNaCl toolchain and distribute your application through the Chrome
+Web Store, and thereby take advantage of the conveniences of PNaCl, such as not
+having to explicitly compile your application for all supported architectures.</p>
+<h2 id="when-to-use-nacl"><span id="id5"></span>When to use NaCl</h2>
+<p>Use NaCl if any of the following apply to your application:</p>
 <ul class="small-gap">
-<li>PNaCl does not support architecture-specific
-instructions in an application (i.e., inline assembly), but tries to
-offer high-performance portable equivalents. One such example is
-PNaCl&#8217;s <a class="reference internal" href="/native-client/reference/pnacl-c-cpp-language-support.html#portable-simd-vectors"><em>Portable SIMD Vectors</em></a>.</li>
-<li>PNaCl only supports static linking with the <code>newlib</code>
-C standard library (the Native Client SDK provides a PNaCl port of
-<code>newlib</code>). Dynamic linking and <code>glibc</code> are not yet supported.
-Work is under way to enable dynamic linking in future versions of PNaCl.</li>
-<li>PNaCl does not support some GNU extensions
-like taking the address of a label for computed <code>goto</code>, or nested
+<li>Your application requires architecture-specific instructions such as, for
+example, inline assembly. PNaCl tries to offer high-performance portable
+equivalents. One such example is PNaCl&#8217;s <a class="reference internal" href="/native-client/reference/pnacl-c-cpp-language-support.html#portable-simd-vectors"><em>Portable SIMD Vectors</em></a>.</li>
+<li>Your application uses dynamic linking. PNaCl only supports static linking
+with a PNaCl port of the <code>newlib</code> C standard library. Dynamic linking and
+<code>glibc</code> are not yet supported in PNaCl. Work is under way to enable dynamic
+linking in future versions of PNaCl.</li>
+<li>Your application uses certain GNU extensions not supported by PNaCl&#8217;s LLVM
+toolchain, like taking the address of a label for computed <code>goto</code>, or nested
 functions.</li>
 </ul>
 </section>