This article was previously published under Q65662
Microsoft Windows version 3.0 sets the WINDIR environment variable whenever
any program, including a MS-DOS program, is run under it. WINDIR is set to
the directory where WIN.COM is found. This is usually C:\WINDOWS. The
WINDIR variable is removed from the MS-DOS environment when you exit
Windows.
As a result, MS-DOS applications can detect whether they are running under
Windows. If WINDIR is set to a valid name, the application is running under
Windows.
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