Multilevel Queue Scheduling and Priority Scheduling

In operating systems, scheduling is an essential component responsible for allocating system resources efficiently. It governs the order in which processes are executed and ensures fairness, responsiveness, and optimization of system performance. There are various scheduling algorithms available, each designed to address specific requirements and priorities. In this article, we will explore two such scheduling algorithms: Multilevel Queue Scheduling and Priority Scheduling.

Multilevel Queue Scheduling

Multilevel Queue Scheduling is a scheduling algorithm that categorizes processes into multiple queues based on specific criteria, and each queue is assigned a priority level. Each queue operates independently with its own scheduling algorithm, allowing processes with different priority levels to be scheduled differently.

The most common implementation of Multilevel Queue Scheduling involves three major queues, namely:

  1. Foreground Queue: Contains interactive processes that require immediate user attention. This queue usually employs round-robin scheduling to provide fair execution to each process.

  2. Background Queue: Consists of long-running processes, such as print spooling, file compression, or system backups. These processes are assigned a lower priority and are usually scheduled using a First-In-First-Out (FIFO) scheduling algorithm.

  3. Batch Queue: Includes processes that require minimal user interaction, such as large data processing or system maintenance tasks. Batch processes are scheduled using a priority scheduling algorithm where priority levels determine the order of execution.

By categorizing processes into different queues, Multilevel Queue Scheduling ensures that processes with higher priority get relatively more CPU time, while still allowing lower priority processes to execute in a fair and timely manner.

Priority Scheduling

Priority Scheduling, as the name implies, assigns a priority value to each process and schedules them based on the assigned priority. The process with the highest priority is given the highest preference for CPU allocation. Priority values can be fixed or dynamically assigned based on specific characteristics or requirements.

There are two types of priority scheduling algorithms:

  1. Preemptive Priority Scheduling: In this type, the currently executing process can be preempted by a higher priority process that arrives in the ready queue. Preemptive priority scheduling ensures that urgent and critical processes are given immediate attention, even if it means interrupting the execution of lower priority processes.

  2. Non-preemptive Priority Scheduling: In this type, once a process starts executing, it continues until completion or it voluntarily releases the CPU. The CPU is not preempted by a higher priority process, allowing the current process to finish its execution.

Priority Scheduling algorithm is highly flexible and can be tailored to various scenarios by adjusting the assigned priorities. It is commonly used in real-time systems, where time constraints and criticality determine the process priorities.


Multilevel Queue Scheduling and Priority Scheduling are two significant scheduling algorithms used in operating systems. Multilevel Queue Scheduling allows for the categorization of processes into different queues based on their priority level, ensuring fairness and responsiveness. On the other hand, Priority Scheduling assigns priority values to processes, determining their order of execution. Each algorithm serves different purposes and can be applied depending on the specific requirements and priorities of the system.

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