$Notebooks (Built-in Mathematica Symbol)

$Notebooks is True if Mathematica is being used with a notebook-based front end.

$OperatingSystem (Built-in Mathematica Symbol)

$OperatingSystem is a string giving the type of operating system under which Mathematica is being run.

$Output (Built-in Mathematica Symbol)

$Output gives the list of files and pipes to which standard output from Mathematica is sent.

$OutputSizeLimit (Built-in Mathematica Symbol)

$OutputSizeLimit specifies the maximum size in bytes of expressions that will automatically be output in their entirety in a Mathematica notebook.

$ParentProcessID (Built-in Mathematica Symbol)

$ParentProcessID gives the ID assigned to the process which invokes the Mathematica kernel by the operating system under which it is run.

$PerformanceGoal (Built-in Mathematica Symbol)

$PerformanceGoal gives the default setting for the option PerformanceGoal for graphics and other algorithmic functions.

$ProcessorType (Built-in Mathematica Symbol)

$ProcessorType is a string giving the architecture of the processor on which Mathematica is being run.

$ReleaseNumber (Built-in Mathematica Symbol)

$ReleaseNumber is an integer which gives the current Mathematica kernel release number, and increases in successive releases.

$SoundDisplayFunction (Built-in Mathematica Symbol)

$SoundDisplayFunction gives the default setting for the option DisplayFunction in sound functions.

$SystemCharacterEncoding (Built-in Mathematica Symbol)

$SystemCharacterEncoding gives the default raw character encoding for the computer system on which Mathematica is being run.