Imagine how different the computing world would be if IBM had used proprietary chips in the original PC, rather than off-the-shelf components. The PC clone market would never have happened, and IBM, rather than Microsoft, might have emerged as the leading company of the computer revolution.

Or if Steve Jobs had never taken his fateful tour of Xerox PARC? Had he not seen PARC's GUI in action he might never have created the Macintosh. And then where would Windows be today?

In every industry there are key milestones that mark a change in the course of history, and the fast-moving technology field has more than its share. Presented here are 15 turning points that shaped the computing world as we know it today, including some that still continue to influence its direction for years to come.

Apple's NeXT Move
In the late 1990s, Apple was in bad shape. Its image was tarnished, its market share was declining, and Windows NT and Windows 95 had outpaced the aging Mac OS in features and technology.

Apple's top-secret new OS, codenamed Copland, could restore Apple's technological lead—if it ever shipped. After 10 years of development, it had swelled into an overambitious boondoggle.

In 1996, with no release date for Copland in sight, then-CEO Gil Amelio made one of the toughest decisions in Apple's history. Abandoning the Copland money-pit, he acquired upstart NeXT, which not only had its own, Unix-based OS that could be modified to run on the Mac but also Apple co-founder Steve Jobs as its CEO.

Reunited, Jobs proceeded to reinvent Apple. His successes included not just Mac OS X, but the iMac, the iPod, and a winning line of servers, workstations, and portables. The decision did lead to Amelio's departure, but the legacy of his NeXT move is a radically different Apple than the one he joined.

Xerox and the Dawn of Free Software
You think you have printer problems? Consider this: In 1980, programmers at MIT's artificial intelligence lab, blessed with one of Xerox's newest laser printers, had to run upstairs to check whether a print job was finished because the machine had been installed on the wrong floor.

No problem, thought one MIT hacker. He'd simply modify the printer's software to automatically e-mail users when their jobs were completed. He'd done it before, for earlier Xerox printers; all he needed was the printer's source code. But something had changed. Citing copyright and trade secrecy, Xerox wouldn't release the code for its newest machine without a signed nondisclosure agreement—an unheard-of request at the time.