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.
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.