On Tuesday, Apple introduced Safari 4, a preview version of its web browser for Mac OS X and Windows. Although it has a far smaller market share than Microsoft Internet Explorer or even Mozilla Firefox, past versions of Safari have been able to run circles around their competitors as far as absolute speed and reliability. The performance gap was big enough that I declared Safari 3 my favorite browser in this column last year.

But what does this new version have to offer? First and foremost, Safari 4 pushes the bar on performance even higher. The new Nitro JavaScript engine results in a substantial improvement in page load times for pages that use JavaScript extensively. Since JavaScript is the bread and butter of many new-age web applications like Google’s Gmail and Google Maps, this is a great boon to the many web surfers that visit these useful sites.

Also in this vein, Safari 4 brings support for next-generation web standards, such as the next version of the Hypertext Markup Language (HTML, used to define the structure of web pages) and Cascading Style Sheets (CSS, which define web pages’ appearance). It is one of the first browsers to pass the Acid3 test, a widely respected metric for how well a browser complies with standards, with a perfect mark of 100 — for comparison, the current pre-release versions of Internet Explorer and Firefox get a 20 and 94 respectively. This is great news, as these new standards will enable a lot of exciting new functionality on your favorite web sites, so the more our major browsers strive to implement them correctly, the better.

Safari 4’s new interface features were prominently seen in Google’s Chrome browser, which was introduced to the public in September and still has not made it to Mac OS X. Probably the most visible change was the relocation of the tab bar to the top of the browser window, where the title bar used to be. This takes a bit of getting used to, but it frees up the visible area of the browser to display more of the page you’re looking at. Apple has also introduced a new “top sites” screen that displays your most visited sites in a graphical grid. Top Sites has the capability to remove sites you don’t like and to pin certain sites to the menu so that they will always be shown, regardless of the frequency of visits. The graphical approach has also found its way into other parts of Safari, with the history and bookmarks features now sporting Apple’s signature Cover Flow browser that was first seen in iTunes and then OS X 10.5.

All in all, Safari 4 is a huge upgrade. It’s still a beta, so there are a number of bugs that can cause crashes; keep this in mind before you install it on your own systems. However, Apple has raised the bar again, and hopefully Microsoft and Mozilla will attempt to catch up with their own offerings.