Just three weeks after the release of Platform Preview 6, Microsoft has released a seventh preview of Internet Explorer 9. The highlight of this new release is not new standards compliance but rather performance.

Improved performance has been a key goal of Internet Explorer 9's development. The new browser version relies heavily on GPU acceleration to provide high-speed graphics rendering and animation, and it includes a new JavaScript engine, codenamed Chakra, that compiles JavaScript in the background to achieve JavaScript performance that's tens or hundreds of times faster than Internet Explorer 8.

Throughout the development process, Microsoft has emphasized that the focus is on real-world website performance, not on popular but narrow benchmarks like the SunSpider JavaScript benchmark. Internet Explorer 9's SunSpider performance has improved over the course of its development, but the company says that this has been a side-effect of its real-world focused improvements rather than a deliberate objective.

Even if SunSpider wasn't the main goal, the browser's performance is impressive: with the new beta, Microsoft is claiming better performance than Chrome 8 beta, Opera 11 alpha, and Firefox 4 beta 7, making the company's JavaScript performance the best around. This should be taken with a pinch of salt; there are some indications that Internet Explorer 9 is, for one reason or another, optimizing some benchmarks functions particularly aggressively but not performing similar optimizations to near-identical functions. This might indicate a bug in its optimizer, or it could indicate cheating.

The timing of this release is a little surprising. Previous previews were released at a frequency of about one every eight weeks. The gap between this release and the previous one is much shorter. Redmond says that the release frequency is driven by the company's desire to ensure that each new release shows a meaningful improvement over its predecessor. It happens that the performance work the developers have been doing has yielded a meaningful improvement in just three weeks, so that's why the release is being made now.

As a performance-focused release, this new version doesn't include a new set of HTML or CSS test cases. The company has updated a small number of the existing tests to resolve bugs in them, but the overall standards conformance should be essentially identical to that of Platform Preview 6.

Platform Preview 7, like previous previews, ships without a real user interface. The instructions we gave for Platform Preview 6 to couple the new engine with the Internet Explorer 9 beta user interface should still work with the new build, making its use a great deal more pleasant.