From the 'browser speed wars' files:

Apple is out with the first public beta of its Safari 4 web browser with a claim of running JavaScript 4.2 times faster than Safari 3. JavaScript isn't the only thing that makes a browser faster but it's a technology measurement that all browser vendors lately are competing on.

The general idea is that modern web sites use a lot of JavaScript and as such the faster a browser can deal with JavaScript, the faster the browsing experience will be for the user.

In its official press announcement for Safari 4 beta Apple claimed that its new Nitro JavaScript engine," .. executes JavaScript up to 30 times faster than IE 7 and more than three times faster than Firefox 3. Safari quickly loads HTML web pages three times faster than IE 7 and almost three times faster than Firefox 3."

Apple does not make any mention of its relative performance against Google Chrome (which like Apple uses the WebKit rendering engine) or Opera. Mozilla is currently working on the TraceMonkey JavaScript engine for Firefox 3.1 which in my opinion will likely serve to change the results. Microsoft too has made speed improvements with its IE 8 browser so the gap between Safari and IE is likely to be a whole lot narrower.

Beyond speed, Safari 4 includes some HTML 5 support and new CSS functionality that web developers will notice. On the end user facing side Apple has taken a page from Chrome's playbook with a Top Sites feature that shows users which sites they've most frequently visited.

Apple has also improved Search with a full history search that looks through web addresses and titles to help users find what they're looking for.

"Apple created Safari to bring innovation, speed and open standards back into web browsers, and today it takes another big step forward," said Philip Schiller, Apple's senior vice president of Worldwide Product Marketing in a statement. "Safari 4 is the fastest and most efficient browser for Mac and Windows, with great integration of HTML 5 and CSS 3 web standards that enables the next generation of interactive web applications."

Safari isn't just for Apple Mac users either. The new beta is also available for Windows too (though no Linux version).