complex instruction set computer. Traditional computer architecture that operates with large sets of possible instructions. Most computers are in this category, including the IBM compatible microcomputers. As computing technology evolved, instruction sets expanded to include newer instructions which are complex in nature and require several to many execution cycles and, therefore, more time to complete. Computers which operate with system software based on these instruction sets have been referred to as complex instruction set computers. Contrast with reduced instruction set computer [RISC].