1981 was the birth year of the IBM PC, as well as MS-DOS that would lay the foundation for the mainstream computer as we know it today. MS-DOS was based on Q-DOS, which was programmed by Seattle Computer Products. What is now known as one of the most ingenious business decisions of the computer world, Microsoft acquired the rights to the software for $75,000 and licensed it to IBM. The licensing terms as well as the success of the IBM-PC which was offered with MS-DOS (renamed to PC-DOS on IBM-PCs) established Microsoft as a leading software company. MS-DOS development was continued until 2000, but was used by Microsoft since the mid-1990s as a more and more invisible layer below its graphical Windows user interface, even if DOS command access was provided via a dedicated DOS window.