Simulation Of First Come First Served FCFS

Any modification on the scheduling algorithm will appear as modification on the operating system kernel code. Processor is an important source of CPU scheduling process, so it becomes very important on accomplishing of the operating system design goals. A delicate problem of the well-functioning of SO is the case when in CPU comes two or more processes which wants to be executed. Scheduling includes a range of mechanisms and policies that SO has to follows in order that all processes take the service.

In this Paper we will discuss about two main batches algorithms, such as FCC and SF, and I will how a manner how to improve these algorithms in the future work. Keywords - CPU-Scheduling, Scheduler, OFFS, SF. 1. Introduction CPU scheduling is important because when we have multiple renewable processes, it can have a big effect on resource utilization and the overall performance of the system [2]. C.

I Latency time: that is the time it takes for the dispatcher to stop one process and start another running CPU scheduling deals with the problem of choosing a process from the ready queue to be executed by the CAP]. In a scheduling process is the responsibility of scheduler to determine when a recess moves from running state to waiting state also scheduler passes a process from the ready state to the execution state[J. In general waiting queues use FIFO and LIFO policies. We have two types of scheduling algorithms preemptive and non-preemptive.

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It's preemptive in those cases where the execution of a process can be interrupted by another process (which may have higher priority), while non-preemptive when a process takes control of the CPU and do not leave it until the end of execution The performance of scheduling is linked to several parameters: CPU Usage: CPU should be kept busy at 100% of time . 2. Throughput : Number of process that typically ends executing in the given moment of time . 3. Turnaround time: time which is necessary for the execution of a process. 4. Waiting time: it is time that a process must wait in queue ready to be executed. . Response time : is the time between the reception of the request made , to the first response . We have three types of schedulers: A-Long-term scheduler -? This type of scheduler decides which jobs or processes would be admitted to the ready queue. Also this Scheduler dictates what processes are to run on a system. B-Mid-term Scheduler - One second type scheduler it's mid-term scheduler who removes process from main memory and moves on secondary memory. C-Short-term Scheduler (also known as dispatcher) Dispatcher module gives control of the CPU to the process selected by the short-term scheduler.

Characteristic for dispatcher is the. In order to have an optimal scheduling should be completed follows Eng conditions: 445 1 . CPU-usage - MAX 2. Throughput - Max 3. Turnaround time- MIN 4. Waiting time ; MIN 5. Response time -? MIN[6]. And this is illustrated in Figure 1 that is a four state diagram of OFFS. Is an algorithm non-preemptive so if process take control of CPU and don't leave it until the end of execution. 2. Related Works The scheduler algorithms offer an endless field of study.

I am focused on algorithms batch, I chose these algorithms because windows is very prevalent in my country and I think that this paper will help those who study windows as SO -What that concretely will deal in this paper is the simulation of two algorithms ( in order to compare them ) his topic well has studied by [2] on paper published in 201 1, it has become an excellent study from both theory and practice , Alkali Pant has achieved interesting conclusions regarding the: turnaround time, waiting time and response time time which has a great importance in batch systems.

Another study that is very interesting is [1 3] , Jerry Breeches describes the way that we can get a process attached to a processor . Fig. 1: First Come First Serve Scheduling Figure 2 gives the flow chart of PC'S in which the C code is supported , which we will use for simulation[4]. There is a simple structure hat represents the algorithm from the functional and construction. Processes are added one after another in the ready queue and executed in sequential order in time independently by the burst time they have [2].

Another study in which based my paper is [1 2] . In this paper Minus Lee explains the problems that appear during scheduling process ,he treats the scheduling process improvement, reducing turnaround time ,waiting time response time and. According to the [1 2] different applications require different optimization criteria as example : batch systems (throughput, turnaround time) , interactive system (response time, fairness, user expectation) . Dry. R. B. Gar in his study [3] explains very clearly idea of scheduling through figures.

Others studies that have studied very carefully are [1] , [4] and [6] which helped me to reach a clearer conclusion of waiting time which is important in batches sister. This simulation will be carried through a C code. After I realize this simulation and I calculated the time needed for comparison I have describe a way to improve these algorithms by performance. 3. Theory of Experiment Below will give an overview of algorithms for both instruction and operation. This part will be accompanied by tables and figures to make clear how the functionality of these novo algorithms are. 3. F-CIFS OFFS is the simplest algorithm on batch systems as for the building as for the functioning. Policy that uses this algorithm is that FIFO, so the first process which requires CPU takes seen. 'ice independently by the size of the process Fig. 2: First Come First Serve flow chart Below present the Gaunt diagram for the three processes for which we have calculated average time. 446 Table . 1 Process Execution Process Duration Order 0 Arrival Time 7 2 4 3 A scheduler adds on the top of the queue a process who has a short extenuation time and those who have longer extenuation time into the tail of the queue.

This requires advanced knowledge or assumptions about the time needed to complete the process [1]. Fig. 3: Gaunt chart for First Come First Serve As we see from the Gaunt Chart : Pl waiting time -O PA waiting time = 20 PA waiting time = 27 The average waiting time =(0+20+7)/3=9 Advantages OFFS Is an algorithm relatively easy to understand and build, choosing of process for execution is very simple, enough to take the first in the queue and also the processes are added at the end of the queues. Fig. : Shortest First scheduling Basis for part Of the experiment will be the flow chart. At the flow chart of SF figure 5 is very clear the logic, processes will be executed after they are selected preliminarily. Disadvantages Through put is very low this because the long process want a long time to be executed, this leads to the so-called monopolizing of CPU.

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