Hard to believe, but it's been exactly 30 years since MS-DOS (Microsoft Disk Operating System) came into being. On July 27, 1981, Microsoft bought DOS from Seattle Computer Products for the tidy sum of $75,000. Although MS-DOS didn't make its consumer debut until the following year, the unassuming piece of software went on to become the foundation for Windows, provided the platform upon which Microsoft's empire was built, and helped make Bill Gates the richest man in the world. From the historic first issue of PC Magazine, we re-present our interview with Gates about MS-DOS, where he explains the finer details of the OS and reveals how much influence he personally had over the software that would redefine computing.