JES2 queues the jobs submitted to it in priority order. Use the various initialization statements and parameters to control input device characteristics such as input streams, job classes and their attributes, job priorities, whether to initially hold the job, or a job's default performance group. You can change the attributes of jobs coming into this system through the JES2 input service exits 2, 3, 4, 20, 50, 51, 52, 53 and 54. To enable these exits, see z/OS JES2 Installation Exits.