What is First-Come-First-Served (FCFS) Scheduling  

This is a non-preemptive technique. A single queue of ready processes is maintained, and the dispatcher always picks the first one. This method does not emphasises throughput, since long processes are allowed to monopolise CPU, For the same reason, the response time with FCFS can be high (with respect to execution time), especially if there is a high variance in process execution times. It's fairly obvious that this method penalises short processes following long ones, though no starvation is possible.
http://www.cim.mcgill.ca/~fr anco/OpSys-304-427/lecture-not es/node41.html

Answered by Nishu's at 4:02 PM on October 29, 2008

A first-come-first-serve ("FCFS") scheduler that routes requests from two or more clients to a single resource. The FCFS scheduler contains a time stamp mechanism which provides a time stamp for each request. The scheduler provides resource access to the client with the oldest generated request and under a predetermined priority scheme in the event of simultaneous requests. The time stamps are generated by adders which add the current value of a time stamp counter with the number of client requests. The time stamp counter is incremented by the output of the adders. The updated value of the counter is decoded into a time stamp output value stored within time stamp registers. A hifind circuit reads the registers and generates an output signal associated with the set of registers, and corresponding client request, with the lowest time stamp. The output signal allows the client to access the resource

Answered by Sanjeev at 3:38 PM on October 28, 2008

Well Ashish! This expression describes the principle of a queue processing technique or servicing conflicting demands by ordering process by first-come, first-served (FCFS) behaviour: what comes in first is handled first, what comes in next waits until the first is finished, etc.

Thus it is analogous to the behaviour of persons queueing (or "standing in line", in common American parlance), where the persons leave the queue in the order they arrive, or waiting one's turn at a traffic control signal. FCFS is also the shorthand name (see Jargon and acronym) for the FIFO operating system scheduling algorithm, which gives every process CPU time in the order they come. In the broader sense, the abstraction LIFO, or Last-In-First-Out is the opposite of the abstraction FIFO organization, the difference perhaps is clearest with considering the less commonly used synonym of LIFO, FILO—meaning First-In-Last-Out. In essence, both are specific cases of a more generalized list (which could be accessed anywhere). The difference is not in the list (data), but in the rules for accessing the content. One sub-type adds to one end, and takes off from the other, its opposite takes and puts things only on one end.[1]

A priority queue is a variation on the queue which does not qualify for the name FIFO, because it is not accurately descriptive of that data structure's behavior. Queueing theory encompasses the more general concept of queue, as well as interactions between strict-FIFO queues.

http://en.wikipedia.org/ wiki/FIFO

Answered by Kumaar at 2:44 PM on October 28, 2008

First come, first served (FCFS)

This is a non-preemptive technique. A single queue of ready processes is maintained, and the dispatcher always picks the first one. This method does not emphasises throughput, since long processes are allowed to monopolise CPU, For the same reason, the response time with FCFS can be high (with respect to execution time), especially if there is a high variance in process execution times. It's fairly obvious that this method penalises short processes following long ones, though no starvation is possible.

Answered by NIVEDITA at 11:00 AM on October 28, 2008

Other names of this algorithm are:

* First-In-First-Out (FIFO)
* Run-to-Completion
* Run-Until-Done

Perhaps, First-Come-First-Served algorithm is the simplest scheduling algorithm is the simplest scheduling algorithm. Processes are dispatched according to their arrival time on the ready queue. Being a nonpreemptive discipline, once a process has a CPU, it runs to completion. The FCFS scheduling is fair in the formal sense or human sense of fairness but it is unfair in the sense that long jobs make short jobs wait and unimportant jobs make important jobs wait.

FCFS is more predictable than most of other schemes since it offers time. FCFS scheme is not useful in scheduling interactive users because it cannot guarantee good response time. The code for FCFS scheduling is simple to write and understand. One of the major drawback of this scheme is that the average time is often quite long.

The First-Come-First-Served algorithm is rarely used as a master scheme in modern operating systems but it is often embedded within other schemes.

Answered by jaivir at 9:09 AM on October 28, 2008