Apple has updated its website with a short preview of features coming in the next major update to Mac OS X. But with a Lion Developer Preview in the wild, a few other details are beginning to leak out as well. We wanted to run down what we know so far about the OS update from both official and unofficial sources.

Apple discussed a few of these features, which combine "the power of Mac OS X with the magic of iPad," when it first showed an early preview of Lion last October. Those features include the Mac App Store (available to Snow Leopard users with the 10.6.6 update); Launchpad, a Springboard-like app launcher for Mac OS X; and the ability of apps to run in full-screen mode. There was also Mission Control, a blend of Spaces, Exposé, Dashboard all mashed up.

Official new features

On Apple's website, the company detailed Lion's improved support for multi-touch gestures using a trackpad. In addition to more ways to swipe, pinch, zoom, and more, one notable change is that scrolling now works as it does on iOS devices—drag up on the trackpad to scroll down, drag down to scroll up—complete with "rubber-band" effects at the end of scrollable areas. (Edit: the up/down description was backwards, sorry guys! It's fixed now.) This is in contrast to all previous versions of Mac OS X, where dragging down scrolls up and vice versa.

Apple mentioned auto-save and auto-resume features last fall, but didn't go into much detail about them. Now we know that apps updated for Lion will gain the ability to autosave all documents as changes are made. Documents can be locked to prevent inadvertent changes, and Apple said that documents will be "auto-locked" after two weeks. Lion also includes automatic file versioning, saving the state of a document every hour it is open and allowing you to step back to any previous state in a graphical Time Machine-like experience. You can go back through previous versions to revert to a previous state or copy and paste data from an older version into the current one.

Apps updated for Lion also gain the ability to automatically save state whenever they quit. When reopened, the application appears as it did when quit, including any open documents and windows. Lion can automatically resume any open applications whenever you need to log out or reboot. This is especially useful for getting back up and running after performing an OS update, for instance, lessening the pain of lost productivity and increasing the likelihood that important updates get installed instead of ignored.

Apple also disclosed three major new feature additions for Lion on Thursday. One is that Lion will include a new version of Mail that uses a vertical list of e-mails on the left and a full message view on the right, à la iPad. Apple says this new layout works better for widescreen displays and many users of plug-ins for previous versions of Mail that re-arrange the panes in this way would likely agree.

The new version of Mail also includes a new "conversation" view, which displays all e-mails in a particular thread in a single chronological list. It appears to work similar to the conversation view in Gmail, but unlike Gmail it doesn't appear to show your own replies along with e-mails sent to you from others.

Lion will include a new file-sharing feature called "AirDrop." AirDrop allows you to view a list of logged-in users of compatible Macs connected to the same network. To transfer a file to any user, you can just drag-and-drop a file to their name in the list, transferring it directly to that user's Downloads folder. If a logged-in user is in your address book, you'll see their contact photo, making it easier to identify the right target on a crowded network.

However, the most surprising revelation from Apple is that Mac OS X Server will no longer be a separate product. Mac OS X Lion will include all the necessary services and easy configuration to set up any Mac as a server. It includes all the usual server services, such as user and group management, push notifications, file sharing, calendaring, mail, contacts, chat, Time Machine, VPN, web, and wiki services. A new "Profile Manager" will enable easier set up and management of Mac OS X and iOS devices, integrating with existing directory services. Lion's WebDAV services will automatically allow iPad users to share files remotely, and Lion will also include an updated version of Wiki Server.

Developer preview leaks

Other details about the Lion update are leaking out based on information discovered in the developer preview.

Lion will include an application sandboxing mechanism that appears to be similar to iOS, which helps prevent coding errors like buffer overflows from being exploited to take control of an entire system. Some issues have been found in the current implementation: applications using sandboxing may have trouble using Services and open documents that are renamed in the Finder won't save correctly.

Lion has support for high pixel density monitors using a limited form of resolution independence. Apple has attempted to graft resolution independence onto Mac OS X as far back as 10.4, though the feature was never fully implemented. Lion will reportedly allow developers to use the same "2x" resolution method used in iOS to simultaneously support older 480 x 320 displays as well as the latest generation 960 x 640 Retina displays. Dubbed "HiDPI display modes," displays that have sufficiently high pixel densities will use the higher quality 2x images for UI elements like buttons and icons. Doing so prevents these elements from shrinking to an impossibly small size as pixel densities increase.

Chatter among developers is that Lion has a new, re-written Finder. This Finder reportedly has new ways of viewing files, including automatic grouping by file types such as "text files," "images," or even "source code."

The overall user interface of Lion includes a number of changes to buttons, tab bars, menus, radio buttons, and other elements. Many of the changes appear to be inspired by similar elements in iOS and not unlike design cues seen in the latest versions of iTunes and the Mac App Store.

Other design tweaks abound as well. Many of Mac OS X's included applications have gotten an iPad-style makeover as well, including Address Book, iCal, and the aforementioned Mail. Scroll bars are also not shown by default, only appearing after a scroll gesture or scroll wheel causes a view to scroll. Translucent, iOS-like scroll bars hover over the right side of a scrollable view, similar to the effects used in Twitter for Mac and Sparrow.

Developers have long speculated that such changes would work their way into Mac OS X. "I could see a gradual, slow merger between iOS and Mac OS X styles and approaches," Panic's Cabel Sasser told Ars last summer. "It doesn't make sense for them to be developing two of everything, one good, one not as good—two calendars, two address books—it's got to merge somehow."