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Job control manages computer tasks by allowing one process to use resources in one area while another process uses resources in a different area. Early work control systems were developed to alleviate speed problems, but modern job control systems focus on pre-calculation and prioritization. The computer scheduler maintains a queue of processes and suspends less important ones when more important ones show up.
Job control is the term for managing various actions on a computer system. Computers are capable of doing many things at once, but in many cases only a single process can operate in a given area at a time. Computers use a job control system to manage their tasks, allowing one process to use resources in one area while another process uses resources in a different area. These systems monitor the priority of operations and keep important tasks running faster and less important tasks in the background.
Work control systems were developed early in modern computer design to alleviate speed problems. In many early systems, the central computer systems were more than capable of speeding up the tasks assigned to them. Speed issues occurred in communications with peripheral systems. Not only were the systems slower, but the transfer time between groups of systems was quite long. Additions to peripheral hardware, such as buffers and cache systems, have only made some processes faster and have not fixed the problem.
Multitasking was one of the first attempts at work control. The computer has been given a new system that keeps track of active and inactive jobs. When a system was too busy to handle new work, it was placed in an idle queue. When the hardware was able to run a new process, the higher priority process would be activated. This process would then move into hardware.
The problem with this system was in its decentralized nature. While a single queue contained all active and inactive processes, the hardware information came from the hardware itself. The driver for the hardware reported whether or not it was available to the scheduler: if a process went into an error state and continued to use the hardware, it would never be available. Also, some processes needed only the central processor or a certain peripheral; this would tie up the whole system until those processes finish. To combat this problem, modern labor control systems have been designed.
Job control focuses on the idea of pre-calculation. Each process is assigned an overall priority and occasionally sub-priorities related to particular systems. The computer scheduler maintains the queue of processes. When a more important process than the currently active one shows up, the active one will be suspended and the new process will take over. When the suspended program is the most important process, it will be restarted.
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