How do operating systems allocate CPU resources among processes?

Operating systems allocate CPU resources among processes through a technique known as scheduling.

In more detail, scheduling is a fundamental function of an operating system. It is the method by which work specified by some means is assigned to resources that complete the work. The resources may be network bandwidth, main memory, running time on the CPU, or access to other resources. In the context of CPU resources, the operating system determines which processes are to run, when they are to run, and how much CPU time they are allocated.

There are several different types of scheduling algorithms that an operating system can use, each with its own advantages and disadvantages. These include First-Come, First-Served (FCFS), Shortest Job Next (SJN), Priority Scheduling, Round Robin (RR), and Multilevel Queue Scheduling.

First-Come, First-Served is the simplest scheduling algorithm. In this scheme, the process that requests the CPU first is allocated the CPU first. The disadvantage of this scheme is that short jobs may have to wait for very long jobs to complete before they get a chance to run.

Shortest Job Next is a scheme in which the process with the smallest total CPU requirement is selected next. This scheme minimises waiting time for all processes.

Priority Scheduling is a scheme that uses a priority system to determine which process is executed next. Each process is assigned a priority, and the CPU is allocated to the process with the highest priority.

Round Robin is a scheme that gives each process a slice of time on the CPU, known as a time quantum, before moving on to the next process. This ensures that all processes get a fair share of the CPU's time.

Multilevel Queue Scheduling is a more complex scheme that separates processes according to their CPU usage into different queues. Each queue has its own scheduling algorithm, and the operating system determines which queue to use based on a variety of factors.

In conclusion, the operating system plays a crucial role in managing CPU resources. It uses scheduling algorithms to determine how to allocate these resources among the various processes that need them.