In the span of five years, Microsoft Corp. promised its most advanced operating system ever and then yanked key features to meet deadlines that were missed anyway. Details of what would later be known as Windows Vista sounded suspiciously like Apple’s Mac OS X.

Yet Vista, which finally appears on store shelves and new PCs next Tuesday, manages to largely overcome its long, tortured prelude. Though it duplicates some of the feel and functions of the Mac software, Vista includes its own improvements that take security, reliability and usability to new heights on the PC.