Signaling that it's ready to begin broader beta testing of its next web browser, Microsoft released the fourth and final developer-oriented Internet Explorer (IE) Platform Preview release. IE 9 PP4 delivers impressive improvements in performance, thanks to hardware-accelerated text, audio, and graphics, and the integration of the new "Chakra" JavaScript engine.

"The fourth Platform Preview of Internet Explorer 9 shows the opportunity of fully hardware-accelerated HTML5," Microsoft General Manager Dean Hachamovitch wrote in a blog post announcing the release. "You can run new test drive samples that show modern SVG and native JavaScript integration in action. In March, we promised to deliver platform preview releases approximately every eight weeks. With this installment, you will find more performance and more support for the same markup. You'll also find many fixes to issues reported in previous Platform Previews."

IE 9 PP4 also shows continued improvement in industry-standard tests. In the SunSider JavaScript performance benchmark, IE 9 PP4 leaps ahead of Apple Safari 5, coming within striking distance of Google Chrome and Opera. And on the dubious ACID3 test, IE 9 jumps from a score of 83 (out of 100) in PP3 to 95 in PP4. Microsoft notes that the missing five points involve two particular technologies (SVG Fonts and SMIL animation of SVG) that are in transition.

Microsoft previously announced that it would deliver the first end-user beta of IE 9 in September, and the company told me this week it intends to stick to the same schedule during the beta, releasing a new version every eight weeks. In preparation for the beta, Microsoft is calling on web developers to code their sites to target standards and not older IE versions. If websites check for feature compliance rather than browser type, IE 9 will run the same code as Google Chrome and other standards-based browsers, albeit it often at dramatically faster speeds.

"The IE9 platform is nearly complete," Hachamovitch added. "We ask that developers and partners start testing in preparation for the beta and prepare their sites to take advantage of IE9's new capabilities."

To download IE 9 PP4 and check out a new round of performance, HTML 5, and graphics demos, please visit the Microsoft website.