$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.

$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.

$MinPrecision (Built-in Mathematica Symbol)

$MinPrecision gives the minimum number of digits of precision to be allowed in arbitrary-precision numbers.

$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.

$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.