$Display (Built-in Mathematica Symbol)

$Display gives a list of files and pipes to be used with the default $DisplayFunction.

$HomeDirectory (Built-in Mathematica Symbol)

$HomeDirectory gives your "home" directory.

$IgnoreEOF (Built-in Mathematica Symbol)

$IgnoreEOF specifies whether Mathematica should terminate when it receives an end-of-file character as input.

$InitialDirectory (Built-in Mathematica Symbol)

$InitialDirectory gives the initial directory when the current Mathematica session was started.

$InputFileName (Built-in Mathematica Symbol)

$InputFileName is a global variable whose value is the absolute file name of the input file from which input to Mathematica is currently being sought.

$Input (Built-in Mathematica Symbol)

$Input is a global variable whose value is the name of the stream from which input to Mathematica is currently being sought.

$MaxPiecewiseCases (Built-in Mathematica Symbol)

$MaxPiecewiseCases gives the maximum number of cases to allow in explicit Piecewise objects generated by expanding any single piecewise function.

$Notebooks (Built-in Mathematica Symbol)

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

$ProcessorType (Built-in Mathematica Symbol)

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

$SyntaxHandler (Built-in Mathematica Symbol)

$SyntaxHandler is a global variable which, if set, is applied to any input string that is found to contain a syntax error.