With IE9, though, Microsoft is trying to rebuild the browser for the Web that’s to come through new standards such as HTML5 and CSS3, updates to Hypertext Markup Language for describing Web pages and Cascading Style Sheets for formatting.

1^st developer preview of IE9 was launched on March 16, 2010.

The preview is bare bones and doesn’t have much in terms of user interface. Still, it provides a good glimpse into what we can expect from IE9: a complete reboot. It supports HTML5, the new version of the mark-up language that supports more dynamic webpages, video embedding, and geolocation. Microsoft also focused on adhering to web standards. IE9’s Acid3 test — a measure of how well a web browser follows certain web standards — achieves a score of 55/100. Microsoft also shows off its improved compliance with CSS, including rounded corners (if you’ve ever developed for previous version of IE, this is definitely a sore spot). Microsoft also seems intent on being compatible with CSS3, which is currently under development. However, IE9 will not support Windows XP. But it could prove to be a smart move, as it might help push more people to upgrade to Windows 7.

May 5 2010: 2^nd developer preview of IE9 released.

The new preview offers a higher ACID 3 test score, 68 out of 100, and there’s a 117-millisecond improvement in speed according to Webkit.org’s SunSpider benchmark tests. Microsoft didn’t provide exact numbers for context.

Webkit.org's SunSpider Performance Update

Microsoft promised improved performance and graphics support, and the company said it’s been working closely with standards bodies. It submitted 79 new tests to the World Wide Web Consortium (W3C) responsible for HTML 5 compliance, bringing the total to 183.

The 2^nd release builds on the first Platform Preview, delivering improvements to IE9’s performance, support for standards, and hardware acceleration of HTML5.

Another headline element for IE9 is a new JavaScript engine. When it comes to these engines for running Web-based programs, Chrome has V8, Opera 10.5 has Carakan, Safari has Nitro, and Firefox has the new JaegerMonkey.

Now Internet Explorer has its own new name for a JavaScript Engine: Chakra. One big change in the JavaScript engine is its multicore support. As soon as a Web page is loaded, Chakra assigns a processing core to the task of compiling JavaScript in the background into fast code written in the native language of the computer’s processor.

Microsoft has also updated the test drive site with a new set of developer samples to show what developers can do with GPU-powered HTML5. As part of its commitment to enabling developers to use the Same Markup – the same HTML, CSS, and script – on the web, it has contributed many new tests to the W3C for HTML5, as well as CSS3 Media Queries and DOM. The Developer Tools in this preview include some new features to make finding and fixing markup issues easier.

The IE9 Platform Preview itself is a change, too. Previously, Microsoft delivered a more finished product to the world. Now it’s trying to get feedback at an earlier stage of development. And it’s explicitly seeking comment on a wide range of elements.

The platform preview installs side by side with Internet Explorer 8 so that you can try it without replacing the full IE that comes with Windows. This second release of the Internet Explorer 9 Platform Preview will install over the first version. There is no need to uninstall the first Preview before installing second.  You’ll also find more information on what’s included in this release of the Platform Preview in the Release Notes, including known and resolved issues.

You can download the 2^nd developer preview from here.