Break out the beer, MS-DOS turns 30 today. On July 27, 1981, Microsoft purchased QDOS from Seattle Computer Products. It was kind of a good deal.
When IBM came to Microsoft asking for a 16-bit operating system, the company had to scramble to get one together. Rather than writing a new one from the ground up, it turned to Seattle Computer Products and its existing 86-DOS (aka QDOS), and bought a non-exclusive license for $25,000. The next Spring, in May 1981, it hired away the program's author, programmer Tim Paterson. And then, on July 27, it paid another $50,000 for all rights. A month later, it was shipping on IBM personal computers, and eventually turned Bill Gates and Paul Allen into two of the world's richest men.
Just don't blame Paterson for Windows, okay?