$Failed (Built-in Mathematica Symbol)

$Failed is a special symbol returned by certain functions when they cannot do what they were asked to do.

$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.

$InstallationDirectory (Built-in Mathematica Symbol)

$InstallationDirectory gives the top-level directory in which your Mathematica installation resides.

$LicenseExpirationDate (Built-in Mathematica Symbol)

$LicenseExpirationDate is a date list that gives the expiration date for the license under which Mathematica is being run.

$LicenseServer (Built-in Mathematica Symbol)

$LicenseServer is a string that gives the name of the license server that is currently authorizing Mathematica to be run.

$Line (Built-in Mathematica Symbol)

$Line is a global variable that specifies the number of the current input line.

$Linked (Built-in Mathematica Symbol)

$Linked is True if the Mathematica kernel is being run through MathLink.

$MachineID (Built-in Mathematica Symbol)

$MachineID is a string that gives, if possible, a unique identification code for the computer on which Mathematica is being run.

$MachineType (Built-in Mathematica Symbol)

$MachineType is a string giving the general type of computer on which Mathematica is being run.