Presentiaon task sheduling first come first serve FCFS
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This document discusses the First Come First Served (FCFS) CPU scheduling algorithm. FCFS is a non-preemptive algorithm that allocates the CPU to the process that requests it first. It is simple to implement using a first-in first-out queue, but it is not optimal and can result in longer waiting times for shorter processes. While easy to understand, FCFS is not suitable for time-sharing systems due to its non-preemptive nature.
Presentiaon task sheduling first come first serve FCFS
- 1. الرحيم الرحمن هللا بسم Elmashreq University Faculty of engineering Electronics engineering dept Prepared by: supervisor: 1.
- 2. Introduction: Process that requests the CPU FIRST is allocated the CPU FIRST. It’s simplest to understand and the simplest to implement . Other names of this algorithm are: • First-In-First-Out (FIFO) . • Run-to-Completion . • Run-Until-Done . This is a non-preemptive algorithm. Example on real life such as: Buying tickets ! Example on computer system likes: sharing printers. Implementation: • FIFO queues. • A new process enters the tail of the queue. • The schedule selects from the head of the queue.
- 4. Scheduling Algorithms: First-Come, First-Served (FCFS) • Example: Three processes arrive in order P1, P2, P3. – P1 burst time: 24 – P2 burst time: 3 – P3 burst time: 3 • Waiting Time – P1: 0 – P2: 24 – P3: 27 • Completion Time: – P1: 24 – P2: 27 – P3: 30 • Average Waiting Time: (0+24+27)/3 = 17 • Average Completion Time: (24+27+30)/3 = 27 P1 P2 P3 0 24 27 30
- 5. Problems with FCFS: o Non-preemptive. o Not optimal AWT. Cannot utilize resources in parallel: • Assume 1 process CPU bounded and many I/O bounded processes. result: Convoy effect, low CPU and I/O Device utilization. a convoy effect happens when a set of processes need to use a resource for a short time, and one process holds the resource for a long time, blocking all of the other processes. Essentially, it causes poor utilization of the other resources in the system.
- 6. Advantages and Disadvantages: Advantages: • simple • easy to understand • first come, first served Disadvantages: • Non-preemptive, that is, the process will run until it finishes. • short processes which are at the back of the queue have to wait for the long process at the front to finish. • Not good for time sharing systems. • Because of its simplicity, FCFS is not very efficient.