Sequential execution most often found in behavioral descriptions
Statements inside PROCESS execute sequentially
ARCHITECTURE sequential OF test_mux IS
BEGIN
select_proc : PROCESS (x, y, selector)
BEGIN
IF (selector = '0') THEN
z <= x;
ELSIF (selector = '1') THEN
z <= y;
ELSE
z <= "XXXX";
END IF;
END PROCESS select_proc;
END sequential;