After a general description of the major hardware elements of a minicomputer, the system is discussed from the viewpoint of a machine-language programmer. It is shown that the machine imposes certain constraints upon the programmer. These constraints are necessary in order to provide computation capability at a reasonable cost. In order to increase the power of the minicomputer without letting the cost become excessive, techniques have evolved whereby an instruction entering the processor for execution need carry only a portion of the total information required. Through previous instructions the processor has been set up for the current instructions. Microprogramming is viewed as a mechanism for increasing the possible power of a given machine instruction. A natural outgrowth of a setup processor and microprogramming is alterable control store.