This paper describes an operational small computer multiprogramming system developed for the control of the Stanford Two Mile Linear Accelerator (SLAC). The system has many features of larger systems such as dynamic memory allocation and interprocess control, but does not have to handle typical batch type jobs which need large arrays and many other system resources. This difference results in a drastic reduction in the complexity of both design and implementation. The accelerator control problem is discussed in terms of what requirements are imposed on the system by the environment. Then the basic subsystems are described with sufficient examples to show the reader other areas where such a system may be applicable.