$GeoLocation (Built-in Mathematica Symbol)

$GeoLocation is a settable global variable that specifies the default geodetic location to use.

$HistoryLength (Built-in Mathematica Symbol)

$HistoryLength specifies the number of previous lines of input and output to keep in a Mathematica session.

$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.

$ImagingDevices (Built-in Mathematica Symbol)

$ImagingDevices gives a list of available imaging devices.

$ImportFormats (Built-in Mathematica Symbol)

$ImportFormats gives a list of import formats currently supported in your Mathematica system.

$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.

$Inspector (Built-in Mathematica Symbol)

$Inspector is a global variable which gives a function to apply when the inspector is invoked from an interrupt menu.