Apple Computer's new OS X marks the death of one of the world's great operating systems. Rejoice!

 I write this not as an Apple-basher, but as a long-disappointed Macintosh fanatic. Since its birth, the Macintosh has always had an excellent user interface but a crummy underlying operating system. Those problems date back to 1984, when Apple shipped the first Macintosh with Motorola's 68000 microprocessor rather than waiting for the more able-bodied 68010. That choice prevented Apple from incorporating technologies like memory protection and preemptive multitasking into the original Mac. The legacy of that mistake was nearly two decades of system crashes. But all of this history is about to be rendered moot.

With OS X, Apple is making a dramatic departure from the past. OS X (the X means 10) is a fundamentally new operating system that is merely pretending to be a Macintosh of old. This is big news-and not just for Apple users. Indeed, it may be bigger news to people using Microsoft Windows. What makes MacOS and Windows so important is their reach. MacOS is used by tens of millions of people every day, Windows by more than 100 million. These operating systems intimately influence the way people work and think. Their capabilities and limitations set the ground rules of what is possible and profitable for hundreds of thousands of companies. Killing one of these operating systems and replacing it with another cannot help but have far-reaching impacts.

And make no mistake about it-OS X is a different animal. Its visual similarity to earlier Mac systems is only a veneer. Apple's previous operating systems were purebreds, with an unbroken lineage going all the way back to the first Macintosh. OS X is a mongrel. Its foundation is Unix, the operating system that traces its ancestry back to Bell Labs and the late 1960s. And the user interface that sits atop this operating system also comes from outside of Apple; it was developed at NeXT Computers (the company that Steve Jobs started after being kicked out of Apple). OS X can run most existing Macintosh software, but this is done with a kind of computational sleight-of-hand.