Microsoft released MS-DOS in 1981 but there were many related disk operating systems. Games are 16 bit programs using the *COM or *EXE file extension. Programs were originally monochrome and used the keyboard rather than a mouse. Colour was introduced with CGA (16 colours) in 1981, VGA (64 colours) in 1984 and EGA (256 colours) in 1987. DOS games also work on Windows 9x (3.1, 95, 98, ME), OS/2 and eComStation.