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PROCESS, NEW, LONG TERM SCHEDULER, SHORT TERM SCHEDULER, :star: Suppose a…
PROCESS
context
- Process ID
- Process State
- CPU Registers
- Accounts Info
- I/O status info
- CPU Scheduling algo
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A process is a program in execution.
It is a active entity instead of a program which is considered as a passive entity.
NEW
LONG TERM SCHEDULER
READY
SHORT TERM SCHEDULER
RUNNING
I/O Request
WAIT/BLOCK
MEDIUM-TERM SCHEDULER
SUSPEND WAIT/BLOCK
Suppose all the processes are doing their I/O such that the waiting queue is full, then we need to suspend those processes i.e. swap them out of the main memory into the secondary memory using a medium term scheduler.
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Whenever the process requests access to I/O or needs input from the user or needs access to a critical region(the lock for which is already acquired) it enters the blocked or wait state.
- The process remains in the main memory but does not get CPU
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Considering uniprocessor system Out of all the processes in the ready queue Short term Scheduler schedules a single process to be executed and changes it's state.
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MEDIUM-TERM SCHEDULER
SUSPEND READY
Process that was initially in the ready state but was swapped out of main memory and placed onto external storage by scheduler is said to be in suspend ready state
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UNBLOCK
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When the waiting/block state is continuously getting filled then the suspend block processes are made to go to the suspend ready queue state this is also known as backtracking :
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LONG TERM SCHEDULER
Also known as Job Scheduler It ensures that maximum number of processes are moved to the ready queue.
- it regulates the Degree of Multiprogramming.
SHORT TERM SCHEDULER
Also known as CPU Scheduler It ensures which program is suitable or important for processing.
- It regulates the DEGREE OF MULTITASKING
- It regulates less degree of Multiprogramming
:star: Suppose a VIP Process came in ready queue while execution of a process then CPU will stop the execution of the running process and send it back to the ready queue and execute the high priority process
or It may be the case that RR scheduling is been used and the time quantum is reached for that process.
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MEDIUM-TERM SCHEDULER
Also known as Process Swapping Scheduler Responsible for suspending and resuming the process. It mainly does swapping (moving processes from main memory to disk and vice versa)
- reduces the degree of multiprogramming
CONTEXT SWITCHING
process of saving the context(state) of the old process(suspend) and loading it into the new process(resume). It occurs whenever the CPU switches between one process and another.