The platform preview is not a complete browser since it lacks an address bar and some navigation and security features. It's a prebeta release that shows off the IE team's integration of HTML 5 support, scalable vector graphics and hardware-accelerated graphics -- all hallmarks of Microsoft's technology focus with IE 9.
Platform preview 4 of IE 9 can be downloaded at Microsoft's test page here. It runs on Windows 7 and Windows Vista, but it doesn't work with Windows XP.
Dean Hachamovitch, general manager of Internet Explorer, said that this latest IE 9 platform preview is "nearly complete" in a blog post. He asked that designers, developers and partners begin testing platform preview 4 to get ready for the forthcoming beta version. Kevin Turner, Microsoft's chief operating officer, recently said that IE 9 will be released as a beta sometime in September.
Platform preview 4 will be the last test platform issued before the beta release of IE 9.
The big news with this platform preview release is that Microsoft has integrated its "Chakra" JavaScript engine inside IE 9, with the script engine based on ECMAScript 5. Hachamovitch said that the integration improves the browser's performance, and that Microsoft had plowed new ground with this technology.
"Through this deep integration, the performance of real world websites significantly improves, and IE9 becomes the first browser to have a shared DOM [Document Object Module] between the browser and the script engine based on ECMAScript5."
ECMAScript 5 is based on the ECMA-262 specification for enabling client-side scripting in Web browsers. The spec reached the final candidate stage of approval in May of 2009 and has offshoots such as JavaScript and JScript. Hachamovitch said that the integration based on ECMAScript 5 "prepares the entire system for the future." For other scripting languages (such as VBScript), Microsoft plans to use the older model of having the scripting engine interact with the browser's DOM through the Component Object Model (COM).
"IE9 will continue to support additional programming languages through the legacy model, but we strongly encourage developers and enterprises to take full advantage of the benefits of JavaScript moving forward," Hachamovitch explained.
Platform preview 4 showed improved test results according to benchmarks that Microsoft reported. The WebKit SunSpider JavaScript test showed IE 9 platform preview 4 at about the same performance level as other top browsers, beating out Mozilla's Firefox and Apple's Safari in speed results, but still lagging behind Google's Chrome and the Opera browser. Platform preview 4 now scores 95 of 100 on the Acid3 test (100 is a perfect score). However, Microsoft tends to downplay the importance of Acid3, saying that it doesn't test the most commonly used features.
Microsoft's blog includes a table showing a summary of cross-browser testing results. It depicts how well the same code markup runs on various browsers. According to the table, IE 9 platform preview is at near 100 percent compatibility for HTML 5, SVG 1.1, CSS 3, DOM and JavaScript.
Microsoft's main goal with IE 9 has been to unburden developers from having to code for different browsers. In most cases, developers have been coding for quirks based on legacy browser performance, particularly Internet Explorer 6, which is still widely used. Microsoft is now advocating that developers should code for features to take advantage of them when they get supported in browsers. That approach also helps to avoid potential display problems that can occur as browser makers issue various versions of their products.
With the platform 4 release, Microsoft has rolled out new tests. They allow users to compare IE 9 performance with that of other browsers. An overview of the tests is described by Rob Mauceri, group program manager for Internet Explorer.
Josh Rose, program manager for Internet Explorer, shows how hardware acceleration affects audio performance in IE 9 platform preview 4. Patrick Dengler, senior program manager for Internet Explorer, demonstrates scalable vector graphics performance. Native graphics support for the canvas element is demonstrated by Seth McLaughlin, program manager for Internet Explorer.
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