Job scheduling, intermediate scheduling, process scheduling

Job scheduling （ Advanced scheduling ）： Its main task is to select a job from the backup state of external storage according to certain principles （ Or more ） Homework , Allocate memory to them 、 Input / Output devices are marked with resources , And set up the corresponding process , Job scheduling generally exists only in multi-channel batch processing system .
Intermediate dispatch （ Memory scheduling ）： Its function is to improve memory utilization and system throughput . therefore , It is responsible for transferring those processes that cannot run temporarily to external memory to wait , Or redeploy those ready processes that are ready to run on the external memory into the memory again , Hang in the ready queue and wait .
Process scheduling （ Low level scheduling ）： The easiest to distinguish , Its main task is to select a process from the ready queue according to a certain method and strategy , Assign the processor to it , General operating system must be equipped with process scheduling .

The connection of three-level dispatching ：
Job scheduling selects a batch of jobs from the backup queue of external memory to enter memory , Build a process for them , These processes are sent to the ready queue , Process scheduling selects a process from the ready queue , And change its state to running state ,CPU Assigned to it . Intermediate scheduling will suspend those processes that cannot run temporarily , When memory space is loose , Select the process with running conditions through intermediate scheduling , Wake it up .
seeing the name of a thing one thinks of its function , Intermediate scheduling is between job scheduling and process scheduling .