Top 10 List of Week 08

1. CPU Scheduling in Operating System
   CPU scheduling is a process that allows one process to use the CPU while the execution of another process is on hold(in waiting state) due to unavailability of any resource like I/O etc, thereby making full use of CPU. The aim of CPU scheduling is to make the system efficient, fast, and fair.

2. CPU Scheduling Algorithms
   There are mainly six types of process scheduling algorithms:
   • First Come First Serve (FCFS)
   • Shortest-Job-First (SJF) Scheduling
   • Shortest Remaining Time
   • Priority Scheduling
   • Round Robin Scheduling
   • Multilevel Queue Scheduling

3. Preemptive Scheduling
   Preemptive Scheduling is a scheduling method where the tasks are mostly assigned with their priorities. Sometimes it is important to run a task with a higher priority before another lower priority task, even if the lower priority task is still running. At that time, the lower priority task holds for some time and resumes when the higher priority task finishes its execution.

4. Non-Preemptive Scheduling
   Non-preemptive Scheduling is used when a process terminates, or a process switches from running to waiting state. In this scheduling, once the resources (CPU cycles) is allocated to a process, the process holds the CPU till it gets terminated or it reaches a waiting state. In case of non-preemptive scheduling does not interrupt a process running CPU in middle of the execution. Instead, it waits till the process complete its CPU burst time and then it can allocate the CPU to another process.

5. Scheduling in Real Time Systems
   Real-time systems are systems that carry real-time tasks. These tasks need to be performed immediately with a certain degree of urgency. In particular, these tasks are related to control of certain events (or) reacting to them. Real-time tasks can be classified as hard real-time tasks and soft real-time tasks.

6. What is Burst time, Arrival time, Exit time, Response time, Waiting time, Turnaround time, and Throughput?
   Burst time is the total time taken by the process for its execution on the CPU. Arrival time is the time when a process enters into the ready state and is ready for its execution. Exit time is the time when a process completes its execution and exit from the system. Response time is the time spent when the process is in the ready state and gets the CPU for the first time. Waiting time is the total time spent by the process in the ready state waiting for CPU. Turnaround time is the total amount of time spent by the process from coming in the ready state for the first time to its completion.

7. FCFS Scheduling Algorithm
   First Come First Serve (FCFS) is an operating system scheduling algorithm that automatically executes queued requests and processes in order of their arrival. It is the easiest and simplest CPU scheduling algorithm. In this type of algorithm, processes which requests the CPU first get the CPU allocation first. This is managed with a FIFO queue. The full form of FCFS is First Come First Serve.

8. Round Robin Scheduling Algorithm
   The name of this algorithm comes from the round-robin principle, where each person gets an equal share of something in turns. It is the oldest, simplest scheduling algorithm, which is mostly used for multitasking. In Round-robin scheduling, each ready task runs turn by turn only in a cyclic queue for a limited time slice. This algorithm also offers starvation free execution of processes.

9. Priority Scheduling Algorithm
   Priority Scheduling is a method of scheduling processes that is based on priority. In this algorithm, the scheduler selects the tasks to work as per the priority. The processes with higher priority should be carried out first, whereas jobs with equal priorities are carried out on a round-robin or FCFS basis. Priority depends upon memory requirements, time requirements, etc.

10. Shortest Job First Algorithm
    Shortest Job First (SJF) is an algorithm in which the process having the smallest execution time is chosen for the next execution. This scheduling method can be preemptive or non-preemptive. It significantly reduces the average waiting time for other processes awaiting execution. The full form of SJF is Shortest Job First.