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Inside Mac OS X 10.7 Lion: Auto Save, File Versions and Time Machine

Mac OS X 10.7 Lion makes a conceptual leap away from the Mac's original focus on opening apps to create files, launching a new task-centric interface borrowed from iOS. Lion apps can also auto save multiple Versions of the document for Time Machine-like recovery of previous iterations of a file.

Auto Save

Lion-specific apps, just like iOS apps, will largely manage the saving of documents themselves, allowing users to focus on what they're doing rather than managing file system concepts. While still a work in progress, Lion's new Auto Save feature goes beyond just saving a backup copy to prevent lost work (something apps like TextEdit and Microsoft Word already do).

Rather than just automatically saving an alternative background copy at set intervals, Lion's Auto Save feature actually saves documents as a series of differential changes to the same file, making it largely unnecessary to remember to save a new file or to save the file before quitting an app (at least in theory).

This flexibility, already implemented on iOS, focuses the user on the task they want to do, allowing the operating system to take over the tedious task of handling file management. It also allows users to incrementally step back though the changes they've made to a document.


Rather than manually selecting to "Save" a document and then later choosing to "Save As" a separate file, apps designed to take advantage of Auto Save and Versions in Lion will offer to "Save" and "Save a Version," as the new TextEdit does (below).

Lion Versions

A Version is a snapshot of the document in time, not a separate file. Rather than littering the file system with separate versions of a file, changes are recorded to the file as internal Versions along with timestamps of when they were saved. This allows user to essentially undo changes or recover a previous state of the document as it has evolved over time.

Google's online Docs provide a similar type of versioning functionality, implemented as an "undo stack," where users can revert to a previous revision, or view (and copy data from) a previous version for restoring data that was edited out at an earlier point.

It appears Mac OS X Lion's Versions does something similar, based on previous work done for iOS. Apple's iWork iPad apps (Pages, Keynote and Numbers) enable the user to perform a series of undo operations even after closing and reopening a file, indicating that Apple saves each change as the user works, so that each edit can be undone at any future point.

In Mac OS X Lion, file Versions are presented in an interface similar to Time Machine; it depicts the existing version of the document, along with a historical timeline of incremental changes that have been saved as Versions (either manually by the user, or by Auto Save, which is scheduled to save a new version every hour, and also anytime you open the document to begin an editing session.)

Lion Versions

Versions vs Time Machine

With Versions, users can step back through time to recover the previous state of a document, just as if they had saved a new copy of the document on a regular basis and kept backups of all the changed files. Similar to Time Machine's multilink backups, Versions only saves the changes to the document, avoiding duplication of all the data that hasn't changed.

Unlike Time Machine, Versions appends all the change snapshots within the local document file, avoiding a file system mess and the need to access backups from a Time Capsule or other external disk just to revert back to previous Versions created in the last several hours.

Versions also differ from Time Machine in that users aren't just limited to restoring a previous version. Instead, you can bring up the hourly snapshots (or any manually saved Versions) of your document, find a particular paragraph you added several days ago but then subsequently deleted, and then copy just that part out of the old snapshot and drag it into your current version of the document.

While Time Machine helps you step back in time to grab a missing file or contact or other item from your backups, Versions allows you to actually step back through time and selectively browse through the work you've done.

This makes Versions more similar to the "Previous Versions" (Shadow Copy) feature Windows users liked to compare to Time Machine. One difference is that Lion's Versions feature, like Time Machine itself, has been given an easy to use, visual interface.

On page 2 of 2: Versions and Time Machine integration, Auto Save and Version integration, Resume.