Input Queue - Operating System

Operating System

In Operating System’s processes are loading into memory, and wait for their turn to be executed by the Central Processing Unit (CPU). CPU scheduling manages process states and decides when a process will be executed next by using the input queue.

First-Come-First-Serve

First-Come-First-Serve processes are taken out from the queue in consecutive order that they are put into the queue. This method is simple causing poor performance because every process is treated equally. If process A that takes 5 minutes to execute and comes into the queue before process B, which is extremely important, B still has to wait until A finished its job. This method is fair, but it takes long time to process.
Shortest remaining time

Shortest remaining time method tries to predict the processing time of developments and places them into the queue from the smallest to largest processing time. This method estimates and predicts based on prior history records. In term, its performance is not stable but better improves process waiting time than First-Come-First-Serve.
Fixed priority pre-emptive scheduling

Fixed priority pre-emptive scheduling method assigns different priorities to the processes based on their processing time and arranges them into the queue in order of their priorities. CPU server processes from higher to lower priority, and processes which have the same priority are served as First-Come-First-Serve. The CPU will temporary stop serving low priority process when higher priority process coming into the queue.
Round-robin scheduling

Round-robin scheduling method will give a same amount of time for each process and cycle through them. This method is heavily bases on allot time giving to each process. Too short allot time will fragment the processes, and too long allot time will increase waiting time for each process to be executed. Choosing right allot time is the foundation for this method.
Multilevel queue scheduling

Many queues are used in Multilevel queue scheduling method and each queue has its own scheduling algorithm. Multilevel queue scheduling is more complex compare to other methods, but it provides flexibility for OS to serve different data in complicated situation.