Skip to main content

Round-Robin Scheduling in operating system-computer world

 Round-Robin Scheduling in operating system-computer world

Round-Robin Scheduling 

The round-robin(R-R Scheduling) Scheduling algorithm is designed for time sharing operating system. Round-Robin is similar to FCFS Scheduling, but preemption is added to enable the system to switch between processes. In Round-Robin Scheduling a small unit of time is used which is called a time quantum or time slice. A time quantum is generally from 10 to 100 millisecond. The CPU Scheduler goes around the ready queue, allocate the CPU to every process for a time interval of up to 1 time quantum. In this scheduling new processes are added to the tail of the ready queue. The CPU scheduler picks the first process from ready queue, set a timer after one time slice and dispatch the process. One of two things will happens. When a process have CPU burst of less the 1 time quantum. In this case the process itself release the CPU. If the CPU burst time of the currently running process is longer then one time quantum, the will go off . A context will executed, and the process will be put at the tail of the ready queue. The CPU scheduler will the select the next process in the ready queue. The average waiting time under the R-R scheduling is long.  The performance of R-R scheduling is depends on the size the time quantum. In R-R scheduling algorithm, the operating system defines a time quantum. All the process will executed in the cyclic way each process will get the CPU for a small amount of time and then get back to the ready queue to wait for its next turn. The new process is added to the ready queue. Context switching is used to save the processes in PCB. Consider the following set of processes that arrive time 0, with the length of the CPU burst given in milliseconds.

Process                                    Burst Time

 P1                                                             24

 P3                                                              3

 P3                                                              3

In this case we use time quantum of 4 milliseconds, the process p1 gets the first 4 millisecond. Since it require another 20 milliseconds, it is permitted after the first time quantum, and the CPU is given to the next process ,process p2. Process p2 does not need 4 milliseconds, so it quits before it's time quantum expires. The CPU is given to the next process , process p3 once each process received 1 time quantum, the CPU return to the process p1. 

Let's calculate the average waiting time for this schedule. P1 wait for 6 millisecond (10-4), P2 wait for 4 millisecond, p3 wait for 7 millisecond. The average waiting time is 17/3 = 5.66 millisecond.



Comments

Post a Comment

Popular posts from this blog

Deadlock in operating system-computer world

  Deadlock in operating system-computer world Deadlock :  In a multi-programming environment, many process may complete for a minute number of resources. A process make a request for a resource and if the resource is not available at that time, the process enter In a waiting state. A waiting state process is never again-able to change state because the resource it has requested is held by other waiting process. This situation is called deadlock. So we can say that a process is said to be deadlock when it is waiting for an event or resources which will never occurs.   so we can say that in this situation none of the process gets executed  since the resource it needs, is held by some other process which is also waits for some other resource to be released.  Let's assume that there are three process P1, P2, p3 and three different resources R1, R2 and R3. R1 is assigned to p1, R2 is assigned to P2 and R3 is assigned to P3.   After somet...
9 comments
Read more

What is sound card, video card, TV tuner card and network adapter card-computer world

 What is sound card, video card, TV tuner card and network adapter card Sound card :  Sound card is also known as audio card, sound sound board or audio output device. Sound card is a expansion card that provide the input and output of audio signals to and from a computer under control of computer programs. It is an expansion card for producing sound on computer that can be heard by speakers and headphones.  Uses of sound card :  Sound card is used for for providing the audio component  for multimedia application such as video auditing , audio auditing .It is also used in the field of education.  Video card :  It is an expansion card that connect to a computer motherboard. Video card is also known as video adapter or video controller. It is used to create a picture on display. TV tuner card : A  TV tuner card is like a television tuner that allow single to be received by a computer. TV tuner c...
2 comments
Read more

Memory management in operating system-computer world

Memory management in operating system-computer world Memory management :   The function of operating system which manages the memory of a computer for the processing of the program this management is known as memory management. There are several programs that consist in memory, so it became to move programs and data around the memory of a memory management system is the collection of hardware and software procedures for the Managing various program consisting in the memory. Memory management play an important role in operating system to improve the speed speed of the computer system.   Memory management determines how  memory is allocated between the processes,  deciding which gets memory, when they receive it and how much they are allowed. When memory is allocated it determines which memory location will be assigned. Main memory refers to a physical memory that is the internal memory of the computer. Main memory is also known as RAM. The computer is able t...
1 comment
Read more