And to think they started out in 1980 with only one OS...XENIX ,an OS based on UNIX.
"Microsoft announces Microsoft Xenix OS, a portable operating system for 16-bit microprocessors. It is an interactive, multiuser, multitasking system that will run on Intel 8086, Zilog Z8000, Motorola M68000, and DEC PDP-11 series. All of Microsoft's existing system software (Cobol, Pascal, Basic, and DBMS) will be adapted to run under the Xenix system, and all existing software written for Unix OS will be compatible as well. "
--from a Microsoft press release, 1980