The number is already outdated as I write it, but Apple said this morning that more than 11 million copies of Safari 4 have been downloaded in the first three days of its release.

That includes 6 million copies of Safari for Windows, which should be a wake-up call to Microsoft about improving Internet Explorer.

The latest version of Safari, a free browser announced Monday at the Worldwide Developer Conference, has a new Nitro JavaScript engine that Apple says can run JavaScript code eight times faster than Microsoft’s IE 8 and four times faster than Mozilla’s Firefox 3. Safari 4 loads HTML web pages three times faster than IE 8 and three times faster than Firefox 3.

Safari 4 also has new features like Top Sites (which previews frequently visited or favorite web pages), Full History Search (which lets you quickly rotate through your previously visited pages), and Cover Flow, the side-scrolling view borrowed from iTunes. Safari is based on the open source Webkit browser engine. Apple says Safari is the first browser to pass the Web Standards Project’s Acid3 test, which examines how compatible the browser is with dynamic web applications.

As part of Mac OS X Snow Leopard, a new version of Apple’s operating system that debuts in September, Safari 4 runs as a 64-bit application. That helps it run JavaScript 50 percent faster. And if a Safari plug-in crashes, the browser itself will continue to run and only the affected plug-in is disabled.

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