Difference between Multi Level Queue Scheduling (MLQ) and First Come First Served (FCFS)

Processes are scheduled using a variety of algorithms in CPU scheduling. First come first serve (FCFS), Shortest Job First (SJF), Shortest Remaining Time First (SRTF), Priority Scheduling, Round Robin (RR), Multi-Level Queue (MLQ), and Multi-Level Feedback Queue (MLFQ) are just a few of the scheduling algorithms available.

These scheduling algorithms are used to handle operating system scheduling, which is in charge of assigning CPU time to available processes. To increase user interaction, throughput, and real-time response, among other things.

Multi Level Queue Scheduling (MLQ)

It is quite difficult to have just one queue and schedule all the processes. This is where multi level queue scheduling is used. In this the processes are divided into various classes depending upon the property of the processes such as system process, I/O process etc.

Multilevel Queue Scheduling is a CPU scheduling mechanism where the process is divided into several hierarchy queues and each queue possesses a different priority, and process type. The scheduling algorithm can be different for each Queue and these processes are mapped in a permanent manner to a particular Queue following some criteria, for example in relation to priority or resources.

Advantages of Multilevel Queue CPU Scheduling

• Low Scheduling Overhead: Since processes are permanently assigned to their respective queues, the overhead of scheduling is low, as the scheduler only needs to select the appropriate queue for execution.
  
• Efficient Allocation of CPU Time: The scheduling algorithm ensures that processes with higher priority levels are executed in a timely manner, while still allowing lower priority processes to execute when the CPU is idle. This ensures optimal utilization of CPU time.
  
• Fairness: The scheduling algorithm provides a fair allocation of CPU time to different types of processes, based on their priority and requirements.

Disadvantages of Multilevel Queue CPU Scheduling

• Some processes may starve for CPU if some higher priority queues are never becoming empty.
• It is inflexible in nature.
• There may be added complexity in implementing and maintaining multiple queues and scheduling algorithms.

First Come First Served (FCFS)

First Come First Served (FCFS) is the simplest CPU scheduling algorithm, where processes are executed in the order they arrive. It uses a queue data structure to manage the ready queue.

The process at the front of the queue is allocated the CPU, and execution begins. A new process entering the system is added to the end of the queue. Each process runs to completion before the next one starts.

Advantages of FCFS scheduling algorithm

• FCFS algorithm is simple, easy to implement into any preexisting system, and easy to understand.

• Better for processes with large burst time as there is no context switch involved between processes.

• It is a fair algorithm as priority is not involved, processes that arrive first get served first.

Disadvantages of FCFS scheduling algorithm

• Convoy effect occurs i.e. all small processes have to wait for one large process to get off the CPU.

• It is non-preemptive, the process will not release the CPU until it finishes its task and terminates.

Difference between FCFS and Multi Level Queue Scheduling