CPU Scheduling

FCFS Tabular Method

The usual method of computing average time, average wait time, turnaround time and average turnaround time for processes is to make a Gantt Chart and then compute these times.In this article, we explore another way to compute the average turn around time and average wait time for processes based on the same logic given by the …

Shortest Remaining Time First (SRTF)

The shortest job first (SJF) algorithm is preemptive or non-preemptive. You have learned about the non-preemptive SJF in the previous article. In this article, you will learn about preemptive SJF, also called the shortest remaining time first scheduling algorithm. A new process arrives at the ready queue while an old process is executing in the …

Multilevel Queue

A multilevel queue is suitable when the processes are classified in groups. The multilevel queue scheduling algorithm partition the queue into several separate queues. Each of the processes are permanently assigned to one queue based on some property such as memory requirement, process priority, or process type. Then each queue has its own scheduling algorithm. …

Priority Scheduling

A scheduling algorithms like round-robin treat all processes as same. But if we consider other information about a process, some process is more important than the other. This is the motivation behind priority scheduling. Each process carries a priority and process with the highest priority will be allocated CPU time. Since there is a chance …

Shortest-Job-First ( SJF )

The shortest job first algorithm associates the length of the next CPU burst with each process. The CPU time is assigned to a process with the smallest next CPU burst time. If there are two processes with the same next CPU burst time, then FCFS algorithm is applied to them. Consider an example, where the …

Round Robin

The round-robin scheduling algorithm is suitable for time-sharing computers which are similar to FCFS. However, preemption is added to this algorithm to switch between processes. A time slice is defined called time quantum which is typically 10 to 100 milliseconds. The processes are allocated CPU time up to 1-time quantum. Then the process is preempted …

First Come, First Served (FCFS)

The first come first served (FCFS) is the simplest CPU-scheduling algorithm. The process which requests CPU first will be allocated CPU first and so on. The process enters the ready queue and its PCB is linked to the tail of the queue. When the CPU is free, it is assigned a new process from the …

Types of Schedulers

The multi-programming technique wants high CPU utilization by executing some process all the time. The time-sharing computer keeps switching among processes so that all users can interact with their running programs. A process scheduler does the selection of processes for execution on CPU. But there are challenges in multi-programming, if a process has to wait …

Process Scheduling Criteria

The single processor system, one process runs, and other processes wait until CPU is free. In a multiprocessor system, some process always runs and thus increases the CPU utilization. If a process is waiting for the completion of some task, or I/O request, the CPU remains idle. To stop wasting CPU time, the CPU switch …