Unix is usually thought of as an operating system that is used by servers and very technically-oriented people. What many Apple product users don’t realize is that they are using Unix every day.
Unix was, according to Wikipedia, first developed in 1969, which, in computing terms, is several lifetimes. There are countless variations of Unix-like operating systems, such as Linux; Apple’s is called Darwin, and it’s the “core OS” of every Mac, iPhone, iPad, iPod Touch, and AppleTV. (Mac OS X 10.5 is also one of the few operating systems certified as Unix by the organization that owns the trademark.)
How did this happen? Well, back in the seventies and much of the eighties, personal computers were too limited to be able to run a complex OS like Unix. And so computer vendors often developed their own operating systems, as Apple did when they developed the Macintosh.
In the mid-nineties, Mac OS had gone as far as it could go; nothing could be done to it that would, for example, keep it from crashing regularly. After failing to successfully develop a new operating system, Apple bought NeXT, the company Steve Jobs founded when he was ousted from Apple in 1985. NeXT had great technology, though very expensive, and the company never rose above an insignificant blip. Steve Jobs himself was considered part of computing’s past, not present.
This made NeXT attractive to Apple, who wanted NeXT’s OPENSTEP operating system for the foundation of the Mac OS of the future — which we now know as Mac OS X. And OPENSTEP was a derivative of Unix.
Four months later, Steve Jobs was once again running Apple. And today, you’ve got an OS with a long and rich history in your pocket.