However, Microsoft did not actually "open sourced" the code, as it remains under a copyright license, which allows access "solely for non-commercial research, experimentation, and educational purposes," prohibits redistribution, prohibits use of any part of the code in another program, and limits citation of the code in written works to 50 lines.
In 1980, Microsoft provided the BASIC language interpreter for IBM. However, they had other plans and asked Microsoft to create an operating system. Microsoft licensed an operating system from Seattle Computer Products which would become the foundation for PC-DOS and MS-DOS.
Following on the heels of MS DOS, Microsoft released the first DOS-based version of Microsoft Word in 1983, which was designed to be used with a mouse. However, it was the 1989 release of Word for Windows that became a blockbuster for the company and within four years it was generating over half the revenue of the worldwide word-processing market.