Complex instruction set computer
A complex instruction set computer (CISC) is a computer with a processing unit which can perform individual instructions involving many steps. Normally there is special logic associated with each instruction, called microcode. The microcode can itself be considered a computer program.
The advantage of a CISC processor is that it is easier to program than a Reduced instruction set computer. The disadvantage is that the CISC runs somewhat slower because of the extra level of logic. As computer designs mature, the distinction between the reduced (RISC) and complex (CISC) processors tends to be somewhat blurred, but the concepts remain important in computer design.