DOS mode may refer to any of the following:
1. On a Microsoft Windows computer, DOS mode is a true MS-DOS environment. For example, early versions of Windows, such as Windows 95 allowed the user to exit from Windows and run the computer from MS-DOS. Doing this allowed older programs written before Windows or computers with limited resources to run a program. Today, all versions of Windows only have a Windows command line, which lets you navigate the computer through a command line.
2. On an Apple Macintosh computer, you may get a message about DOS Mode when downloading a file or trying to open one that isn't compatible with macOS. For example, executable files that end with .exe are not formatted for the macOS and can only run from within Windows. Make sure you are downloading a file meant for Apple users, otherwise you need to run Windows from within Boot Camp if you expect to run a Windows program.