SAN FRANCISCO--Chrome took several big steps toward becoming a legitimate operating system today, as Google announced major OS improvements to kick off the second day of Google I/O 2011.

When the Chrome OS laptops made by Samsung and Acer ship in the U.S. on June 15, they'll work offline and offer file management support that includes Web app handlers. Developers will also be able to charge users for apps in the Chrome Web Store and offer people in-app purchases.

Google Music running in the Chrome OS.

Sundar Pichai, senior vice president for Chrome, noted that offline support was returning to Chrome OS. Running Chrome OS (beta download) offline will allow you to access Google Docs, Google Calendar, and Gmail without an Internet connection, something Chrome used to be able to do with Google Gears, until the company decided to phase out that project. This will go a long way toward appealing to people who want to continue using their computers when there's weak or zero Wi-Fi or 3G access, such as on airplanes.

The new file manager delves into new territory for the operating system and addresses the glaring lack of local file browsing when the operating system debuted last winter on the Cr-48. The file manager will retain Chrome's style of opening new windows as tabs, though you can still open them in a new window or "rip" the tab off to create a separate window.

The Chrome OS file manager looks similar to those in Windows and Mac, with breadcrumb-style folder navigation at the top, a list of files below that, and a preview pane on the right. Below the preview pane are live options that change based on the type of file you've highlighted. If you click on a photo, you'll get options to open with Google Docs and save to Box.net, but you'll also see a button to upload the image directly to Google's photo-sharing site, Picasa, or open it in the local image viewer. While Box.net is supported now, Google did mention that Dropbox support is expected in the near future.

Chrome OS&39's new file manager.

The file manager will function in Chrome OS as it does in other operating systems. You'll be able to play back music and video files and to one-click copy files from a USB stick or drive to the cloud. It was difficult to discern at the keynote presentation how functional the preview pane is. Certainly, clicking on a file will show it in the preview pane, but there didn't appear to be any instant preview of uploaded files during the keynote demonstration.

One nifty trick that was mentioned is the ability to register Chrome Web apps to handle local files. This means that if you click on a PDF, it will open in the Adobe Reader Web app. It's not immediately clear when that feature will launch, nor is it currently known how it will interact with third-party programs. However, it appears that music and media files will play in a built-in media player. Video playback can now do full screen, too. Streaming media is also a possibility in Chrome OS, including support for the new Google Music, revealed yesterday.

In-app purchasing via the Chrome Web Store was the third big Chrome OS news of the day. It creates a system of one-touch purchases, designed to return the user back to the app as soon as the purchase is completed, and it takes far less out of developer's pockets than Apple does. Apple charges 30 percent, while Google charges only 5 percent, though that comparison isn't quite apples-to-apples since Chrome OS hasn't even been officially released yet. To use the payment system, registering with Google Checkout is required, though if you're using a Chromebook, Google figures you're heavily tied into its systems regardless.

Google also mentioned other changes to the operating system. Pichai said the company had knocked down the Chrome OS start-up time to about 8 seconds. Just like Chrome-the-browser, Chrome-the-operating-system will automatically update every few weeks. Apps will also automatically update, preventing degradation and security issues. Of course, instant updates is one of the big draws of the browser-based operating system, taking complicated concerns like security and stability out of the end-user's control.

In a press conference after the keynote presentation, Pichai also noted why the default Android browser wasn't labeled "Chrome," though his logic was a bit circular. He said, "The Android browser isn't branded as Chrome because they're not the same, although we do share code when we can." Chrome OS, the Chrome browser, and the Android browser all use the V8 JavaScript engine.