Job scheduler
A job scheduler is a computer application for controlling unattended background program execution of jobs. This is commonly called batch scheduling, as execution of non-interactive jobs is often called batch processing, though traditional "job" and "batch" are distinguished and contrasted; see that page for details. Other synonyms include batch system, distributed resource management system (DRMS), distributed resource manager (DRM), and, commonly today, workload automation (WLA). The data structure of jobs to run is known as the job queue. Modern job schedulers typically provide a graphical user interface and a single point of control for definition and monitoring  of background executions in a distributed network of computers. Increasingly, job schedulers are required to orchestrate the integration of real-time business activities with traditional background IT processing across different operating system platforms and business application environments. "Job scheduling" should not be confused with process scheduling, which is the assignment of currently running processes to CPUs by the operating system. Overview. Basic features expected of job scheduler software include: If software from a completely different area includes all or some of those features, this software can be considered to have job scheduling capabilities. Most operating systems, such as Unix and  Windows, provide basic job scheduling capabilities, notably by at and batch, cron, and the Windows Task Scheduler. Web hosting services provide job scheduling capabilities through a control panel or a webcron solution. Many programs such as DBMS, backup, ERPs, and BPM also include relevant job-scheduling capabilities. Operating system ("OS") or point program supplied job-scheduling will not usually provide the ability to schedule beyond a single OS instance or outside the remit of the specific program. Organizations needing to automate unrelated IT workload may also leverage further advanced features from a job scheduler, such as: These advanced capabilities can  be written by in-house developers but are more often provided by suppliers who specialize in systems-management software. Main concepts. There are many concepts that are central to almost every job scheduler implementation and that are widely recognized with minimal variations: Jobs, Dependencies, Job Streams, and Users. Beyond the basic, single OS instance scheduling tools there are two major architectures that exist for Job Scheduling software. History. Job Scheduling has a long history. Job Schedulers have been one of the major components of IT infrastructure since the early mainframe systems. At first, stacks of punched cards were processed one  after the other, hence the term "batch processing". From a historical point of view, we can distinguish two main eras about Job Schedulers: In terms of the type of scheduling there are also distinct eras: Scheduling. Various schemes are used to decide which particular job to run. Parameters that might be considered include: