The Unix Foundation of OS X
Unix is the established, super-reliable OS that powers most of the high-performance servers that make up the Internet. Unix has built-in support for virtually every hardware device ever wrought by the Hand of Man (including all the cool stuff that came with your iMac), and Unix is well designed and highly efficient.
Unfortunately, standard Unix looks at least as hideous as DOS (the original PC operating system), complete with a confusing command line, so ease of use for normal human beings goes out the door. Enter the genius types at Apple, who understood several years ago that all Unix needed was a state-of-the-art, novice-friendly interface!
To wit: OS X was developed with a Unix foundation (or kernel), so it has the same reliability and performance as Unix. However, the software engineers at Apple (who know a thing or two about ease of use) also made it good looking and easy to use.
This is the secret to the worldwide fever over OS X: It blends the best of Unix with the best of earlier Macintosh operating systems like Mac OS 9. OS X is not only easy to use but also runs tight, concentric, sassy rings around anything that Microsoft has to offer today.