{"id":3282,"date":"2025-06-06T14:04:29","date_gmt":"2025-06-06T14:04:29","guid":{"rendered":"https:\/\/diznr.com\/?p=3282"},"modified":"2025-06-06T14:04:29","modified_gmt":"2025-06-06T14:04:29","slug":"day-01-part-17a-schedulers-in-operating-system-long-term-short-term-and-midium-schedulers-term","status":"publish","type":"post","link":"https:\/\/www.reilsolar.com\/pdf\/day-01-part-17a-schedulers-in-operating-system-long-term-short-term-and-midium-schedulers-term\/","title":{"rendered":"Day 01 Part 17(A)- Schedulers in operating system long term, short term and midium term schedulers."},"content":{"rendered":"

Day 01 Part 17(A)- Schedulers in operating system long term, short term and midium term schedulers<\/p>\n

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\u00a0Schedulers in Operating System (OS) \u2013 Long-Term, Short-Term & Medium-Term Schedulers<\/strong><\/h3>\n

Schedulers in an Operating System (OS)<\/strong> are responsible for managing process execution by selecting processes to run in the CPU. There are three types of schedulers<\/strong>:<\/p>\n

Long-Term Scheduler (Job Scheduler)<\/strong>
Short-Term Scheduler (CPU Scheduler)<\/strong>
Medium-Term Scheduler (Swapper)<\/strong><\/p>\n

\u00a0Long-Term Scheduler (Job Scheduler)<\/strong><\/h3>\n

Function:<\/strong> Selects which processes should be admitted into the ready queue<\/strong> from the job pool.
Frequency:<\/strong> Runs infrequently<\/strong> (e.g., once every few seconds or minutes).
Main Purpose:<\/strong> Controls degree of multiprogramming<\/strong> (number of processes in memory).
Works in:<\/strong> Batch Systems<\/strong> (e.g., old mainframe systems).
Example:<\/strong> If there are 100 processes in the job pool<\/strong>, the long-term scheduler chooses 10<\/strong> to bring into RAM.<\/p>\n

Key Role:<\/strong> Determines which programs enter execution<\/strong>.<\/p>\n

\u00a0Short-Term Scheduler (CPU Scheduler)<\/strong><\/h3>\n

Function:<\/strong> Selects which process will execute next in the CPU<\/strong> from the ready queue.
Frequency:<\/strong> Runs very frequently<\/strong> (millisecond level).
Main Purpose:<\/strong> Decides which process gets CPU time<\/strong> for execution.
Works in:<\/strong> All systems (Batch, Time-Sharing, Real-Time<\/strong>).
Example:<\/strong> A process in the ready queue gets scheduled every few milliseconds<\/strong> for execution.<\/p>\n

Key Role:<\/strong> Improves CPU utilization & response time<\/strong>.<\/p>\n

\u00a0Medium-Term Scheduler (Swapper)<\/strong><\/h4>\n

Function:<\/strong> Removes some processes from memory (swaps out) and brings them back later (swaps in).
Frequency:<\/strong> Runs occasionally<\/strong>, based on memory needs.
Main Purpose:<\/strong> Reduces memory load<\/strong> and improves CPU efficiency<\/strong>.
Works in:<\/strong> Time-Sharing & Virtual Memory Systems<\/strong>.
Example:<\/strong> If RAM is full<\/strong>, it moves an inactive process to disk<\/strong> (swap space) and loads an active process.<\/p>\n

Key Role:<\/strong> Manages swapping of processes<\/strong> to optimize RAM usage.<\/p>\n

\u00a0Comparison of Schedulers<\/strong><\/h3>\n
\n\n\n\n\n\n\n\n\n\n
Feature<\/strong><\/th>\nLong-Term Scheduler<\/strong><\/th>\nShort-Term Scheduler<\/strong><\/th>\nMedium-Term Scheduler<\/strong><\/th>\n<\/tr>\n<\/thead>\n
Other Name<\/strong><\/td>\nJob Scheduler<\/td>\nCPU Scheduler<\/td>\nSwapper<\/td>\n<\/tr>\n
Purpose<\/strong><\/td>\nSelects which processes enter RAM<\/td>\nSelects which process gets CPU time<\/td>\nManages swapping of processes<\/td>\n<\/tr>\n
Frequency<\/strong><\/td>\nRuns infrequently<\/td>\nRuns very frequently<\/td>\nRuns occasionally<\/td>\n<\/tr>\n
Speed<\/strong><\/td>\nSlowest<\/td>\nFastest<\/td>\nMedium speed<\/td>\n<\/tr>\n
Affects<\/strong><\/td>\nMultiprogramming level<\/td>\nCPU efficiency<\/td>\nRAM usage<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

\u00a0Key Points to Remember<\/strong><\/h3>\n

Long-Term Scheduler<\/strong> \u2192 Decides which jobs enter execution<\/strong>
Short-Term Scheduler<\/strong> \u2192 Decides which job gets CPU time<\/strong>
Medium-Term Scheduler<\/strong> \u2192 Decides which jobs to swap (suspend\/resume)<\/strong><\/p>\n

Would you like examples of scheduling algorithms<\/strong> like FCFS, Round Robin, or Priority Scheduling<\/strong>?<\/p>\n

Day 01 Part 17(A)- Schedulers in operating system long term, short term and midium term schedulers.<\/a><\/h3>\n
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Operating System Concepts (7th Edition) 600 dpi<\/a><\/h3>\n

Here\u2019s a simple, clear explanation<\/strong> of Schedulers in Operating System<\/strong> (Day 01 Part 17(A)) \u2014 covering Long-term, Short-term, and Medium-term Schedulers<\/strong> \u2014 useful for beginners, competitive exams, and CS students.<\/p>\n

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\ud83d\udda5\ufe0f Schedulers in Operating System<\/strong><\/h2>\n

Schedulers are components of the OS that manage process execution<\/strong> by selecting which process will run when and where<\/strong>.<\/p>\n

There are 3 types<\/strong>:<\/p>\n

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\ud83d\udd36 1. Long-Term Scheduler (Job Scheduler)<\/strong><\/h2>\n

\ud83d\udccc Purpose:<\/strong><\/h3>\n

Controls the admission of processes<\/strong> into the system (from job pool to ready queue).<\/p>\n\n\n\n\n\n\n\n\n\n
Feature<\/th>\nDetails<\/th>\n<\/tr>\n<\/thead>\n
Selects<\/td>\nWhich jobs to admit<\/strong><\/td>\n<\/tr>\n
Controls<\/td>\nDegree of multiprogramming<\/strong><\/td>\n<\/tr>\n
Frequency<\/td>\nRuns less frequently<\/strong><\/td>\n<\/tr>\n
Input Queue<\/td>\nJob Pool \u2192 Ready Queue<\/td>\n<\/tr>\n
Involved in<\/td>\nBatch systems<\/strong> mostly<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\ud83d\udd38 Example:<\/strong> Choosing 5 out of 100 stored jobs to bring into memory.<\/p>\n

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\ud83d\udd37 2. Short-Term Scheduler (CPU Scheduler)<\/strong><\/h2>\n

\ud83d\udccc Purpose:<\/strong><\/h3>\n

Selects one process from the ready queue<\/strong> and assigns it to the CPU<\/strong>.<\/p>\n\n\n\n\n\n\n\n\n\n
Feature<\/th>\nDetails<\/th>\n<\/tr>\n<\/thead>\n
Selects<\/td>\nWhich process runs next<\/strong><\/td>\n<\/tr>\n
Controls<\/td>\nCPU execution<\/td>\n<\/tr>\n
Frequency<\/td>\nRuns very frequently<\/strong> (ms level)<\/td>\n<\/tr>\n
Input Queue<\/td>\nReady Queue \u2192 CPU<\/td>\n<\/tr>\n
Works in<\/td>\nAll systems (batch, time-sharing)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\ud83d\udd39 Example:<\/strong> Picks one process to run when a running process finishes or is interrupted.<\/p>\n

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\ud83d\udfe2 3. Medium-Term Scheduler (Swapper)<\/strong><\/h2>\n

\ud83d\udccc Purpose:<\/strong><\/h3>\n

Temporarily removes processes<\/strong> from memory to reduce load (swapping), and brings them back<\/strong> later.<\/p>\n\n\n\n\n\n\n\n\n\n
Feature<\/th>\nDetails<\/th>\n<\/tr>\n<\/thead>\n
Selects<\/td>\nWhich process to suspend\/resume<\/strong><\/td>\n<\/tr>\n
Controls<\/td>\nMemory usage<\/strong><\/td>\n<\/tr>\n
Frequency<\/td>\nRuns occasionally<\/strong><\/td>\n<\/tr>\n
Involved in<\/td>\nSwapping (Suspend\/Resume)<\/td>\n<\/tr>\n
Used in<\/td>\nTime-sharing and multitasking OS<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\ud83d\udfe2 Example:<\/strong> If RAM is full, it swaps a background process to disk.<\/p>\n

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\ud83d\udcca Comparison Table<\/strong><\/h2>\n\n\n\n\n\n\n\n
Scheduler Type<\/th>\nControls<\/th>\nFrequency<\/th>\nQueue Movement<\/th>\nKey Role<\/th>\n<\/tr>\n<\/thead>\n
Long-Term Scheduler<\/td>\nDegree of multiprogramming<\/td>\nLow (Infrequent)<\/td>\nJob Pool \u2192 Ready Queue<\/td>\nJob selection<\/td>\n<\/tr>\n
Short-Term Scheduler<\/td>\nCPU usage<\/td>\nHigh (Frequent)<\/td>\nReady Queue \u2192 CPU<\/td>\nProcess execution<\/td>\n<\/tr>\n
Medium-Term Scheduler<\/td>\nRAM usage<\/td>\nMedium<\/td>\nMemory \u2194 Disk (Swapping)<\/td>\nLoad balancing<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
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\ud83e\udde0 Memory Tip:<\/strong><\/h2>\n

“Long brings in, Short runs, Medium swaps out.”<\/strong><\/p>\n

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\u2705 Summary:<\/h2>\n