A major goal of operating systems is to process jobs while making the best use of system resources. Thus, one way of viewing operating systems is as resource managers. Before job processing, operating systems reserve input and output resources for jobs. During job processing, operating systems manage resources such as processors and storage. After job processing, operating systems free all resources used by the completed jobs, making the resources available to other jobs. This process is called resource management. There is more to the processing of jobs than the managing of resources needed by the jobs. At any instant, a number of jobs can be in various stages of preparation, processing, and post-processing activity. To use resources efficiently, operating systems divide jobs into parts. They distribute the parts of jobs to queues to wait for needed resources. Keeping track of where things are and routing work from queue to queue is called workflow management, and is a major function of any operating system. JES3 considers job priorities, device and processor alternatives, and installation-specified preferences in preparing jobs for processing job output. This IBM® Redbooks® publication describes a JES3 environment that includes the following: - Single-system image - Workload balancing - Availability - Control flexibility - Physical planning flexibility.