Queue Discipline

The order in which customers are served in a queuing system is referred to as queue discipline. In practice, there are several queue disciplines that are used, including:

• First-In-First-Out (FIFO): Customers are served in the order in which they arrive (first-in, first-out). This is the most commonly used queue discipline in retail stores, fast-food restaurants, and other similar establishments.
• Last-In-First-Out (LIFO): Customers are served in reverse order of arrival (last-in-first-out, or LIFO). This discipline is less commonly used than FIFO, but it can be found in some applications, such as a stack of plates in a cafeteria.
• Priority: Customers are served in accordance with their priority level. Customers with the highest priority are served first, followed by customers with lower priority. This discipline is used in situations where certain customers, such as in an emergency room or a customer service call center, must be served before others.
• Random: Customers are served at random.
• Shortest Job first (SJF): Customers are served based on the time required to complete their service, with the shortest jobs served first.
• Processor sharing: Processor sharing means that all customer requests are treated equally and receive an equal share of the server’s time.

Each queue discipline has advantages and disadvantages, so the discipline chosen will be determined by the system requirements and performance objectives.

In general, there is no fixed set of processes that run on systems; thus, measuring the exact processing requirements of processes is impossible. We can, however, measure the distributions of CPU bursts and I/O bursts over the course of a process and derive a mathematical formula that identifies the probability of a specific CPU burst. The arrival rate of processes in the system can be approximated in the same way. The development of queuing theory, a branch of mathematics, resulted from the use of mathematical models for evaluating the performance of various systems. 

The fundamental model of queuing theories is the same as the model of a computer system. Each computer system is represented as a collection of servers such as CPUs and I/O devices, each with its own queue. The article focuses on discussing the Queuing System in Operating System.

The following topics will be discussed here:

1. Components of Queuing System
2. Number of Servers
3. Measures of Performance for Queuing Systems
4. Notation for Queues
5. Queue Discipline
6. Queuing Models

Let’s start discussing each of these topics in detail.