Apple has started seeding Safari 4 preview copies to developers.

The move comes on the heels of Snow Leopard’s unveiling. The new OS will focus on performance and quality, and Safari 4 sounds like it blends right in.

Applesana points out to Apple’s recent press release talking about Snow Leopard and the new additions. “Using media technology pioneered in OS X iPhone, Snow Leopard introduces QuickTime X, which optimizes support for modern audio and video formats resulting in extremely efficient media playback,” Apple’s press release goes. “Snow Leopard also includes Safari,” Apple notes, “with the fastest implementation of JavaScript ever, increasing performance by 53 percent.”

Apple says this will make Web 2.0 applications feel “more responsive.”

Of course, performance will vary based on system configuration, network connection and other factors.

Apple’s benchmark was based on the SunSpider JavaScript Performance test on an iMac 2.8 GHz Intel Core 2 Duo system running Mac OS X Snow Leopard, with 2GB of RAM. Safari 4 also passed the Acid3 test scoring a perfect 100/100 under Mac OS X 10.5.3.

Save web page as web application
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Apple wants to accomplish this with SquirrelFish technology, currently under development for Webkit. SquirrelFish promises 1.6 times faster JavaScript performance as compared to Webkit / Safari 3.1. SquirrelFish is a register-based, direct-threaded, high-level bytecode engine, with a sliding register window calling convention. It slowly generates bytecodes from a syntax tree, using a simple one-pass compiler with built-in copy propagation.

Reportedly, Safari 4 will have the ability to save webpages as “Web Applications.” This new feature allows Safari to save pages like Fluid, a Leopard app that creates Site Specific Browsers. Allegedly, users will also have the ability to choose how new windows will open.

Download : Safari 4.0 Developer Preview