SCG is in the Lagged Fibonacci class of generators. These generators use a basic algorithm of the form X_n = f(X_(n-r),X_(n-s)) mod m; r>s The function f is typically xor, addition, subtraction, multiplication or subtraction with carry. It uses simpler math than a basic LCG, but keeps a larger state.
NOT recommended for serious use; these are included for historical reasons (compatibility with earlier releases).