In 1991, Linus Torvalds, a 21-year-old computer science student at the University of Helsinki, Fin., having just purchased his first personal computer (PC), decided that he was not satisfied with the computer's operating system (OS). His PC used MS-DOS (the disk operating system from Microsoft Corp.), but Torvalds preferred the UNIX operating system he had used on the university's computers. He decided to create his own PC-based version of UNIX. Months of determined programming work yielded the beginnings of an operating system known as Linux that, eight years later, developed into what many observers saw as a genuine threat to mighty Microsoft and its seemingly ubiquitous Windows OS. By 1999 Torvalds had become a cult hero to a devoted band of computer users.