z/OS® provides two job entry subsystems from which to choose: JES2 and JES3. For a system that has only a single processor, JES2 and JES3 perform similar functions: they read jobs into the system, convert jobs to internal machine-readable form, select jobs for processing, process output, and purge jobs from the system. However, for a system that has multiple processors, there are noticeable differences in how JES2 exercises independent control over its job processing functions; each JES2 processor controls its own job input, job scheduling, and job output processing. In contrast, JES3 exercises centralized control over its processing functions through a single global JES3 processor. This global processor provides all job selection, scheduling, and device allocation functions for all other JES3 systems. The centralized control that JES3 exercises provides increased job scheduling control, deadline scheduling capabilities, and increased control by providing its own device allocation. To gain a more complete understanding of the functional differences between JES2 and JES3, see z/OS JES2 Initialization and Tuning Guide and z/OS JES3 Initialization and Tuning Guide.