Google upgraded the beta version of its Chrome browser yesterday, adding integrated bookmark synchronization and boasting of a 30% speed improvement over the current production edition.

Chrome 4.0.223.16, which runs only on Windows XP, Vista or Windows 7, includes the ability to sync bookmarked sites across multiple computers, said Idan Avraham and Anton Muhin, a pair of Google software engineers who announced the beta on a company blog late on Monday.

Bookmark sync requires that all the machines being kept in step run the Chrome beta, and that the user has a Google account, such as a Gmail username and password. The browser syncs bookmarks using Google Docs , the company's Web-based application suite.

There's no way to set the interval between synchronizations, but Avraham and Muhin said that "any changes you make to your bookmarks will appear on all synced computers in just a few seconds." Google is using the same servers based on XMPP (Extensible Messaging and Presence Protocol) that power its Google Talk instant messaging service for Chrome's sync.

Most other browsers can sync bookmarks only with special add-ons, such as the free Xmarks , which is compatible with Microsoft's Internet Explorer (IE), Mozilla's Firefox, Apple's Safari, and Chrome.

Opera Software's Opera is the only other browser that currently offers free built-in bookmark synchronization . Mozilla, however, launched its Weave project in late 2007, and in September of this year updated the synchronization service to version 0.7 .

Avraham and Muhin also touted Chrome 4.0's faster JavaScript rendering speeds. "We've improved performance scores on Google Chrome by 30% since our current stable release, and by 400% since our first stable release," they said, referring to Chrome 3.0, which left beta in mid-September and the original Chrome that Google unveiled 14 months ago .

Google measured its JavaScript speed using rival Mozilla's DOM Core benchmark suite.

Chrome 4.0 is available for Windows only, although Google has been working on versions for Linux and Mac OS X for months. The Mac version -- the latest is 4.0.223.11 -- has remained in Google's "dev" channel since June, indicating its not ready for official beta testing.

A message posted to the Chromium-dev forum by a Google employee, however, indicates that the Mac team is pushing forward. "Our goal for this Friday is to be able to count our Mac P1 M4 release blocker bugs on one hand (we're in the 20s now)," wrote Mike Pinkerton . In Pinkerton's message, "P1" represents the highest-priority bugs, while "M4" is a designation for "Milestone 4."

Chrome accounted for about 3.6% of all browsers used last month, according to just-released data from Web measurement company Net Applications, but Chrome gained more market share in October than either Firefox or Safari.

Chrome 4.0 beta for Windows can be download from Google's Web site.