(Translated by https://www.hiragana.jp/)
Apple - OS X Lion - At the heart of every Mac is one powerful OS.
The Wayback Machine - https://web.archive.org/web/20110609033329/http://www.apple.com:80/macosx/what-is/

OS X. It's what makes a Mac a Mac.

Because we design software that works hand in hand with our hardware, you get a better operating system. Built on a rock-solid UNIX foundation, OS X is engineered to take full advantage of the technologies in every new Mac. And to deliver the most intuitive and integrated computer experience possible.

Hardware and software made for each other.

Since the software on every Mac is created by the same company that makes the Mac, you get a fully integrated system in which everything works together perfectly. OS X works with the processor architecture in your Mac to deliver the best possible performance. Mac notebooks include a Multi-Touch trackpad that lets you pinch, swipe, and tap your way through every app on the system. OS X gives you long battery life by dimming the screen in low-light conditions and even regulating processor activity between keystrokes.

Easy to use and incredibly powerful.

From the desktop you see when you start up your Mac to the applications you use every day, everything is designed with simplicity and elegance in mind. So getting things done is both intuitive and fun. Of course, making amazing things simple takes seriously advanced technologies, and OS X is loaded with them. Not only is it built on a rock-solid, time-tested UNIX foundation that provides unparalleled stability, it also delivers incredible performance, stunning graphics, and industry-leading support for Internet standards.

Secure by design.

OS X doesn’t get PC viruses. And with virtually no effort on your part, the operating system protects itself from other malicious applications. Because every Mac ships with a secure configuration, you don’t have to worry about changing complex settings in order to stay safe. Even better, OS X won’t slow you down with constant security alerts and sweeps. Apple responds quickly to online threats and automatically delivers security updates. And with FileVault 2 in OS X Lion, all the data on your Mac is protected by powerful encryption.

Built for compatibility.

The versatility and power of OS X help a Mac fit in just about anywhere — including Windows networks. Want to transfer your files, photos, and other data from a Windows PC? OS X lets you do that easily. If you want to run Windows on your Mac, you can do that, too. OS X has built-in support for the latest version of Microsoft Exchange Server, so you can use your Mac at home and at work and keep all your messages, meetings, and contacts in one place. OS X works with virtually all of today’s digital cameras, printers, and other peripherals without the need to manually download separate drivers. And it opens popular file types such as JPG, MP3, and PDF, as well as Microsoft Word, Excel, and PowerPoint documents.

Accessible innovation.

OS X comes standard with a wide range of assistive technologies that help people with disabilities experience what the Mac has to offer, including many features you won’t find in other operating systems — at any price. For example, built-in VoiceOver screen-reading technology, available in over 20 languages, makes it possible for those who are blind or have low vision to control their computers using key commands or gestures on a Multi-Touch trackpad. OS X also offers out-of-the-box support for more than 40 braille displays (including Bluetooth displays) and many other accessibility features, such as dynamic full-screen magnification, playback of closed captions, and a scalable screen.

Reliable from the very start.

Just about everything you do on a Mac — even upgrading to the latest version of the OS — is safe and reliable. OS X checks your applications to make sure they’re compatible and sets aside any programs known to be incompatible. If a power outage interrupts your installation, OS X can start again without losing any data. Best of all, upgrading doesn’t require reformatting your drive; you keep all your compatible applications, files, and settings. And if something goes wrong when you’re using your Mac, Time Machine is there to restore your data if needed.

Comes with everything.

OS X comes in a single version that includes a collection of Apple-designed applications. Not only do they let you surf the web, have video and text chats, manage your contacts, and accomplish other day-to-day tasks, they also work together to make you more productive — and let you have more fun. Learn more about featured apps