When Apple took the wraps off Mac OS X a decade ago, it clearly marked a big leap forward from the old Mac operating system. But as Mac users installed that first beta disk, it wasn't exactly clear how big a leap OS X would turn out to be. With ten of updates, innovations, and enhancements under our belt, we can now see how far we've come since Steve Jobs released the Mac OS X Public Beta at the Apple Expo in Paris on September 13, 2000. We now rely on OS X features that early OS adopters probably couldn't even conceive of a decade ago.

But which OS X innovations have been the most significant for the Mac and its users? We put our heads together and came up with a list of ten features--for the tenth anniversary of the OS X beta's release--that we consider to be the most significant contributions to the Mac experience.

Time Machine

Computing is risky business: All hard drives will fail eventually, and people accidentally delete files. Introduced with OS X 10.5, Time Machine was hugely important for one simple reason: It made backing up your data easy--and therefore, something you were much more likely to do.

Sure, the 3D interface may be a little cheesy, and Time Machine can slow down your system. It's also not always easy to find a file when you need it. But Time Machine makes backing up a given. And on top of that, Time Machine backups are great when you're migrating to a new Mac. Those are reasons alone to celebrate this OS X capability.--JONATHAN SEFF

Native PDF support

Apple's Preview app is the visible face of Mac OS X's system-level support for the PDF format. Mac users can easily create PDF files with any program that supports the Print command. Because PDF files recreate the layout of the original document, saving files electronically is now as convenient as printing them, except you're free to save, e-mail, or embed them in other documents without losing their unique look.

Now at version 5, Preview has undergone numerous improvements over time, but its Annotations toolbar, easy selection of columns, and image editing capabilities emphasize its advantage for users.--JACKIE DOVE

Spotlight

Introduced as the desktop search successor to Apple's Sherlock in OS 10.4, Spotlight made waves for its metadata index and instant-search capabilities. The utility's in-depth search allowed users to search inside their files, rather than by name alone. And with Leopard, introducing the calculation of simple math equations and dictionary searches, Spotlight has only grown as a reference and lookup tool.--SERENITY CALDWELL

iChat

IM clients existed before Apple folded iChat into Mac OS X 10.2 in 2002. But iChat upped the ante by integrating with the operating system's address book and mail applications, and an updated version included in Panther added video conferencing capabilities as well. The inclusion of a built-in chat client gave OS X a notable productivity boost--one we experienced first-hand in the Macworld office. We suddenly had a way to communicate with far-flung colleagues and contributors in a way that was more immediate than e-mail and more convenient than the telephone. (Instead of dropping what you were doing to make a phone call, you could keep working in one window while conducting an iChat in the other.) The Mac has made notable in-roads in the workplace during the past decade, and we suspect the presence of a built-in, full-featured messaging tool is one of the reasons why.--PHILIP MICHAELS