Day 01 Part 17(A)- Schedulers in operating system long term, short term and midium term schedulers.
Day 01 Part 17(A)- Schedulers in operating system long term, short term and midium term schedulers
Contents
- 0.1 Schedulers in Operating System (OS) – Long-Term, Short-Term & Medium-Term Schedulers
- 0.2 Long-Term Scheduler (Job Scheduler)
- 0.3 Short-Term Scheduler (CPU Scheduler)
- 0.4 Comparison of Schedulers
- 0.5 Key Points to Remember
- 0.6 Day 01 Part 17(A)- Schedulers in operating system long term, short term and midium term schedulers.
- 0.7 Operating System Concepts (7th Edition) 600 dpi
- 1 🖥️ Schedulers in Operating System
- 2 🔶 1. Long-Term Scheduler (Job Scheduler)
- 3 🔷 2. Short-Term Scheduler (CPU Scheduler)
- 4 🟢 3. Medium-Term Scheduler (Swapper)
- 5 📊 Comparison Table
- 6 🧠 Memory Tip:
- 7 ✅ Summary:
Schedulers in Operating System (OS) – Long-Term, Short-Term & Medium-Term Schedulers
Schedulers in an Operating System (OS) are responsible for managing process execution by selecting processes to run in the CPU. There are three types of schedulers:
Long-Term Scheduler (Job Scheduler)
Short-Term Scheduler (CPU Scheduler)
Medium-Term Scheduler (Swapper)
Long-Term Scheduler (Job Scheduler)
Function: Selects which processes should be admitted into the ready queue from the job pool.
Frequency: Runs infrequently (e.g., once every few seconds or minutes).
Main Purpose: Controls degree of multiprogramming (number of processes in memory).
Works in: Batch Systems (e.g., old mainframe systems).
Example: If there are 100 processes in the job pool, the long-term scheduler chooses 10 to bring into RAM.
Key Role: Determines which programs enter execution.
Short-Term Scheduler (CPU Scheduler)
Function: Selects which process will execute next in the CPU from the ready queue.
Frequency: Runs very frequently (millisecond level).
Main Purpose: Decides which process gets CPU time for execution.
Works in: All systems (Batch, Time-Sharing, Real-Time).
Example: A process in the ready queue gets scheduled every few milliseconds for execution.
Key Role: Improves CPU utilization & response time.
Medium-Term Scheduler (Swapper)
Function: Removes some processes from memory (swaps out) and brings them back later (swaps in).
Frequency: Runs occasionally, based on memory needs.
Main Purpose: Reduces memory load and improves CPU efficiency.
Works in: Time-Sharing & Virtual Memory Systems.
Example: If RAM is full, it moves an inactive process to disk (swap space) and loads an active process.
Key Role: Manages swapping of processes to optimize RAM usage.
Comparison of Schedulers
| Feature | Long-Term Scheduler | Short-Term Scheduler | Medium-Term Scheduler |
|---|---|---|---|
| Other Name | Job Scheduler | CPU Scheduler | Swapper |
| Purpose | Selects which processes enter RAM | Selects which process gets CPU time | Manages swapping of processes |
| Frequency | Runs infrequently | Runs very frequently | Runs occasionally |
| Speed | Slowest | Fastest | Medium speed |
| Affects | Multiprogramming level | CPU efficiency | RAM usage |
Key Points to Remember
Long-Term Scheduler → Decides which jobs enter execution
Short-Term Scheduler → Decides which job gets CPU time
Medium-Term Scheduler → Decides which jobs to swap (suspend/resume)
Would you like examples of scheduling algorithms like FCFS, Round Robin, or Priority Scheduling?
Day 01 Part 17(A)- Schedulers in operating system long term, short term and midium term schedulers.
Operating System Concepts (7th Edition) 600 dpi
Here’s a simple, clear explanation of Schedulers in Operating System (Day 01 Part 17(A)) — covering Long-term, Short-term, and Medium-term Schedulers — useful for beginners, competitive exams, and CS students.
🖥️ Schedulers in Operating System
Schedulers are components of the OS that manage process execution by selecting which process will run when and where.
There are 3 types:
🔶 1. Long-Term Scheduler (Job Scheduler)
📌 Purpose:
Controls the admission of processes into the system (from job pool to ready queue).
| Feature | Details |
|---|---|
| Selects | Which jobs to admit |
| Controls | Degree of multiprogramming |
| Frequency | Runs less frequently |
| Input Queue | Job Pool → Ready Queue |
| Involved in | Batch systems mostly |
🔸 Example: Choosing 5 out of 100 stored jobs to bring into memory.
🔷 2. Short-Term Scheduler (CPU Scheduler)
📌 Purpose:
Selects one process from the ready queue and assigns it to the CPU.
| Feature | Details |
|---|---|
| Selects | Which process runs next |
| Controls | CPU execution |
| Frequency | Runs very frequently (ms level) |
| Input Queue | Ready Queue → CPU |
| Works in | All systems (batch, time-sharing) |
🔹 Example: Picks one process to run when a running process finishes or is interrupted.
🟢 3. Medium-Term Scheduler (Swapper)
📌 Purpose:
Temporarily removes processes from memory to reduce load (swapping), and brings them back later.
| Feature | Details |
|---|---|
| Selects | Which process to suspend/resume |
| Controls | Memory usage |
| Frequency | Runs occasionally |
| Involved in | Swapping (Suspend/Resume) |
| Used in | Time-sharing and multitasking OS |
🟢 Example: If RAM is full, it swaps a background process to disk.
📊 Comparison Table
| Scheduler Type | Controls | Frequency | Queue Movement | Key Role |
|---|---|---|---|---|
| Long-Term Scheduler | Degree of multiprogramming | Low (Infrequent) | Job Pool → Ready Queue | Job selection |
| Short-Term Scheduler | CPU usage | High (Frequent) | Ready Queue → CPU | Process execution |
| Medium-Term Scheduler | RAM usage | Medium | Memory ↔ Disk (Swapping) | Load balancing |
🧠 Memory Tip:
“Long brings in, Short runs, Medium swaps out.”
✅ Summary:
- Long-Term: Decides who can enter the system.
- Short-Term: Decides who runs on CPU next.
- Medium-Term: Decides who stays or swaps in memory.
Would you like:
- A diagram to visualize all 3 schedulers?
- A PDF of notes for revision?
- Practice questions on this topic?
Let me know!