Day 01 Part 17(B)- Concept of schedulers short term, long term and medium term schedulers

Day 01 Part 17(B)- Concept of schedulers short term, long term and medium term schedulers

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In operating systems, schedulers are responsible for managing the execution of processes by determining which process runs at a given time. There are three primary types of schedulers: Long-Term, Medium-Term, and Short-Term. Each plays a distinct role in process management and system performance.

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Long-Term Scheduler (Job Scheduler)

Role: Determines which processes are admitted into the system for processing.

Functions:

• Controls Multiprogramming: Regulates the number of processes in memory to maintain an optimal level of multiprogramming.

• Process Selection: Chooses processes from the job pool and loads them into the ready queue.

• Process Mix: Ensures a balanced mix of I/O-bound and CPU-bound processes to optimize resource utilization.

Characteristics:

• Frequency: Invoked less frequently compared to other schedulers.

• Speed: Slower decision-making process.

• Presence: Not present in all systems; for instance, time-sharing systems like UNIX often lack a long-term scheduler.

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Medium-Term Scheduler (Swapper)

Role: Manages the swapping of processes in and out of main memory to optimize CPU and memory utilization.

Functions:

• Swapping: Temporarily removes (swaps out) processes from main memory to reduce the degree of multiprogramming and later swaps them back in when appropriate.

• Resource Management: Balances memory usage among processes, ensuring efficient utilization.

• Process Prioritization: May adjust process priorities based on their current state or resource requirements.

Characteristics:

• Frequency: Operates at a medium frequency, depending on system load and memory availability.

• Presence: Common in systems that support swapping; not all operating systems implement a medium-term scheduler.

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Short-Term Scheduler (CPU Scheduler)

Role: Selects which process in the ready queue should be executed next by the CPU.

Functions:

• Process Dispatching: Allocates CPU to one of the ready processes.

• Context Switching: Handles the switching of the CPU from one process to another.

• Scheduling Algorithms: Implements algorithms like First-Come-First-Serve (FCFS), Shortest Job Next (SJN), Round Robin (RR), etc., to determine process execution order.

Characteristics:

• Frequency: Invoked very frequently (milliseconds), making rapid decisions.

• Speed: Fastest among all schedulers due to the need for quick decision-making.

• Presence: Essential component in all operating systems.

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Comparative Overview

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For a visual explanation, you might find this video helpful:

Feel free to ask if you need further clarification or examples on any of these schedulers!

Day 01 Part 17(B)- Concept of schedulers short term, long term and medium term schedulers

Operating System – Process Scheduling

Types Of Scheduling