$LicenseID (Built-in Mathematica Symbol)

$LicenseID is a string that gives the license ID under which Mathematica is being run.

$MaxNumber (Built-in Mathematica Symbol)

$MaxNumber gives the maximum arbitrary-precision number that can be represented on a particular computer system.

$MaxPrecision (Built-in Mathematica Symbol)

$MaxPrecision gives the maximum number of digits of precision to be allowed in arbitrary-precision numbers.

$MessageList (Built-in Mathematica Symbol)

$MessageList is a global variable that gives a list of the names of messages generated during the evaluation of the current input line.

$RootDirectory (Built-in Mathematica Symbol)

$RootDirectory gives the root directory of your file system.

Advanced Topics in Algebra (Mathematica Overview)

Complex Polynomial Systems Real Polynomial Systems Diophantine Polynomial Systems

Graphics and Sound (Mathematica Overview)

Basic Plotting Options for Graphics Redrawing and Combining Plots

Graphics as Input (Mathematica Tutorial)

An image is equivalent to its symbolic expression. You can operate on an image as you would on a symbolic expression. This input produces some disks. Type // InputForm after ...

Strings and Characters (Mathematica Overview)

Properties of Strings Operations on Strings Characters in Strings

Two-Dimensional Expression Input (Mathematica Overview)

Moving through Expressions Selecting and Deleting in Expressions Typing Fractions