$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.

$MachineName (Built-in Mathematica Symbol)

$MachineName is a string that gives the assigned name of the computer on which Mathematica is being run, if such a name is defined.

$Packages (Built-in Mathematica Symbol)

$Packages gives a list of the contexts corresponding to all packages which have been loaded in your current Mathematica session.

$ParentLink (Built-in Mathematica Symbol)

$ParentLink is the MathLink LinkObject currently used for input and output by the Mathematica kernel in a particular session.

$ProcessID (Built-in Mathematica Symbol)

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

$SessionID (Built-in Mathematica Symbol)

$SessionID is a number set up to be unique to a particular Mathematica session.

$UserName (Built-in Mathematica Symbol)

$UserName gives the login name of the user who invoked the Mathematica kernel, as recorded by the operating system.

$VersionNumber (Built-in Mathematica Symbol)

$VersionNumber is a real number which gives the current Mathematica kernel version number, and increases in successive versions.

WriteDataSource (DatabaseLink Symbol)

WriteDataSource[name] writes a new HSQL data source name.WriteDataSource[name, database] writes a new data source to database.