std_ulogic_vector type
The std_ulogic_vector type is used for arrays of std_ulogic variables and signals; it's an unresolved version of std_logic_vector.
The basic VHDL logic operations are defined on this type:
and,
nand,
or,
nor,
xor,
xnor.
These must be given two arrays of the same size; they do the operation on ecah position and return another array. The not operation negates each position in the array.