• $OperatingSystem is a string giving the type of operating system under which Mathematica is being run.
• Typical values for $OperatingSystem are "Windows", "MacOSX" and "Unix".
• You can use $OperatingSystem to get an idea of what external commands will be available from within Mathematica.
• $OperatingSystem typically has the same value for different versions or variants of a particular operating system.
• New in Version 2.