Programmers develop microprograms, using basic software tools. A microassembler allows a programmer to define the table of bits symbolically. Because of its close relationship to the underlying architecture, "microcode has several properties that make it difficult to generate using a compiler." A simulator program is intended to execute the bits in the same way as the electronics, and allows much more freedom to debug the microprogram. After the microprogram is finalized, and extensively tested, it is sometimes used as the input to a computer program that constructs logic to produce the same data. This program is similar to those used to optimize a programmable logic array. 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.