Safari 4 has logged 11 million downloads in its first four days of availability, according to figures from Apple.

The company said that downloads have been steady for the Mac and PC versions since the browser was unveiled on Monday at the Worldwide Developers Conference in San Francisco.

"Safari 4 is an incredible success on Mac and Windows, with more than 11 million downloads in the first three days," said Philip Schiller, senior vice president of product marketing at Apple.

"Safari users love the incredible speed and innovative features like Top Sites, Full History Search and Cover Flow."

Roughly six million of downloads have been from Windows users, and the remaining five million for MacOS X systems. Originally released as a Mac-only browser, Apple first made Safari available to Windows users at the 2007 Worldwide Developers Conference.

Among the new features are the ability to view history files in the iTunes 'cover flow' style, and improved archiving of browsing history. The update also fixes 51 security flaws.

Headlining the Safari 4.0 release, however, is the new Nitro JavaScript engine. Apple said that the new engine significantly improves JavaScript performance, and could get even faster when the company releases the 64-bit OS X Snow Leopard update later this year.