Is the note for 'Long, Medium, and Short-Term Scheduling' free to read?

Yes, NotesMedia provides free access to 'Long, Medium, and Short-Term Scheduling' notes for BCA / B.Tech preparation online.

Does this cover the syllabus for Operating System (OS) Notes in English?

Yes, this chapter covers key concepts of 'Long, Medium, and Short-Term Scheduling' under the Operating System (OS) Notes in English syllabus for BCA / B.Tech.

How long does it take to read 'Long, Medium, and Short-Term Scheduling'?

This note is approximately a 15-minute read.

Long, Medium, and Short-Term Scheduling - (BCA / B.Tech)

Long, Medium, and Short-Term Scheduling in Operating System:

In any operating system, scheduling plays a vital role. Scheduling is the process through which the operating system decides which process gets to use the CPU, when, and for how long. This ensures that all processes in the system are handled efficiently and the system's performance remains optimal.

Long-term, medium-term, and short-term scheduling play important roles at different stages of process management. Long-term scheduling decides which processes enter the system, medium-term scheduling controls which processes are kept in memory and which are swapped out, while short-term scheduling determines which process will use the CPU next. The proper coordination of these three types of scheduling helps an operating system run efficiently and ensures that all resources are used correctly.

Scheduling can be divided into three major categories:

Long-Term Scheduling
Medium-Term Scheduling
Short-Term Scheduling

These three types of scheduling are used at different stages of a process's life and their main purpose is to increase system efficiency and maximize CPU usage. Let's understand these three types in detail.

1. Long-Term Scheduling (or Job Scheduling):

Introduction: Long-term scheduling is also known as Job Scheduling. Its main job is to decide how many processes should be allowed into memory to wait in the queue for the CPU. This scheduler primarily brings jobs from the disk into the main memory.

Main Task: It determines which processes from secondary storage (disk) should be brought into main memory (RAM) to be ready for execution. It controls the degree of multiprogramming, which means how many processes are present in memory at one time.
Goal: The long-term scheduler aims to ensure there is a reasonable number of processes in the system so that the CPU can be used effectively. It maintains a balance so that the system is not overloaded, nor is the CPU left idle.
Frequency: The long-term scheduling process is often slow because it involves bringing jobs into memory and is not executed very frequently.
Process: The decision of the long-term scheduler depends on whether processes are CPU-bound (use the CPU a lot) or I/O-bound (use input/output devices a lot). Maintaining this balance leads to better utilization of all system resources.
Benefits: Helps maintain system performance. Ensures a good mix of I/O and CPU-bound processes.
Drawbacks: Since it runs less frequently, it does not provide an immediate response.

2. Medium-Term Scheduling (or Swapping Scheduling):

Introduction: Medium-term scheduling is also known as Swapping Scheduling. Its main function is to temporarily move processes to secondary storage whose execution is not immediately required. This is called swapping.
Main Task: It controls the number of processes present in the system. When there are too many processes, some are swapped out to secondary storage (disk). When a swapped-out process is needed again for execution, it is brought back into memory. This is called swapping in.
Goal: Its main goal is to balance system resources and ensure that important processes get more CPU time for execution. It optimizes memory usage by swapping out inactive processes from memory.
Frequency: It runs more frequently than long-term scheduling but is not as fast as short-term scheduling.
Process: It is helpful when there are many processes in the system and a shortage of memory. It ensures that only necessary processes remain in memory.
Benefits: Ensures proper use of memory. Swaps out non-essential processes without affecting execution.
Drawbacks: The swapping process can be expensive as it involves disk I/O.

3. Short-Term Scheduling (or CPU Scheduling/Dispatching):

Introduction: Short-term scheduling is also known as CPU Scheduling or Dispatching. Its main job is to decide which process gets the CPU and for how long. It is the most critical scheduler for the CPU as it allocates CPU time to all processes.
Main Task: Its job is to select one process from the queue of ready processes and give it control of the CPU. This process happens repeatedly and directly affects system performance.
Goal: The main objective of the short-term scheduler is to maximize CPU utilization and execute processes quickly. It ensures that processes receive CPU time based on priority, turnaround time, and waiting time.
Frequency: It happens very quickly because it needs to be executed after every process finishes or gets blocked.
Process: The short-term scheduler can use various algorithms, such as: FCFS, SJF, Round Robin (RR), and Priority Scheduling.
Benefits: Maximizes CPU usage. Ensures important processes are executed quickly.
Drawbacks: Since it has to run very frequently, it can increase system overhead.

Long, Medium, and Short-Term Scheduling

Long, Medium, and Short-Term Scheduling in Operating System:

In this Chapter