 Even without fully optimal logic, heuristically optimized logic can vastly reduce the number of transistors from the number required for a ROM control store.This reduces the cost of producing, and the electricity consumed by, a CPU.Microcode can be characterized as "horizontal" or "vertical", referring primarily to whether each microinstruction controls CPU elements with little or no decoding (horizontal microcode) or requires extensive decoding by combinatorial logic before doing so (vertical microcode).