FCFS磁盘调度算法

先决条件：磁盘调度算法。

给定一组磁盘磁道编号和初始磁头位置，如果使用“先到先得”(FCFS)磁盘调度算法，则我们的任务是查找为访问所有请求的磁道而执行的查找操作总数。

先来先服务(FCFS)
FCFS是最简单的磁盘调度算法。顾名思义，该算法按请求到达磁盘队列的顺序来接受请求。该算法看起来非常公平，没有饥饿(所有请求都按顺序处理)，但是通常，它不能提供最快的服务。

算法：

1. 让Request数组代表一个数组，该数组存储已按其到达时间的升序请求的音轨的索引。 “磁头”是磁盘磁头的位置。
2. 让我们一一按照默认顺序获取轨迹，并计算轨迹到头部的绝对距离。
3. 以此距离增加总寻道数。
4. 当前服务的轨道位置现在变为新的头位置。
5. 转到步骤2，直到未维修请求数组中的所有轨道。

例子：

Input: 
Request sequence = {176, 79, 34, 60, 92, 11, 41, 114}
Initial head position = 50

Output:
Total number of seek operations = 510
Seek Sequence is
176
79
34
60
92
11
41
114

下表显示了使用FCFS服务请求的曲目的顺序。

因此，总寻道数计算如下：

= (176-50)+(176-79)+(79-34)+(60-34)+(92-60)+(92-11)+(41-11)+(114-41)
= 510

执行：
下面给出了FCFS的实现。请注意，距离用于存储磁头和当前磁道位置之间的绝对距离。

C++

// C++ program to demonstrate
// FCFS Disk Scheduling algorithm
  
#include 
using namespace std;
  
int size = 8;
  
void FCFS(int arr[], int head)
{
    int seek_count = 0;
    int distance, cur_track;
  
    for (int i = 0; i < size; i++) {
        cur_track = arr[i];
  
        // calculate absolute distance
        distance = abs(cur_track - head);
  
        // increase the total count
        seek_count += distance;
  
        // accessed track is now new head
        head = cur_track;
    }
  
    cout << "Total number of seek operations = "
         << seek_count << endl;
  
    // Seek sequence would be the same
    // as request array sequence
    cout << "Seek Sequence is" << endl;
  
    for (int i = 0; i < size; i++) {
        cout << arr[i] << endl;
    }
}
  
// Driver code
int main()
{
  
    // request array
    int arr[size] = { 176, 79, 34, 60, 92, 11, 41, 114 };
    int head = 50;
  
    FCFS(arr, head);
  
    return 0;
}

Java

// Java program to demonstrate
// FCFS Disk Scheduling algorithm
class GFG
{
static int size = 8;
  
static void FCFS(int arr[], int head)
{
    int seek_count = 0;
    int distance, cur_track;
  
    for (int i = 0; i < size; i++) 
    {
        cur_track = arr[i];
  
        // calculate absolute distance
        distance = Math.abs(cur_track - head);
  
        // increase the total count
        seek_count += distance;
  
        // accessed track is now new head
        head = cur_track;
    }
  
    System.out.println("Total number of " + 
                       "seek operations = " + 
                        seek_count);
  
    // Seek sequence would be the same
    // as request array sequence
    System.out.println("Seek Sequence is");
  
    for (int i = 0; i < size; i++)
    {
        System.out.println(arr[i]);
    }
}
  
// Driver code
public static void main(String[] args) 
{
    // request array
    int arr[] = { 176, 79, 34, 60, 
                  92, 11, 41, 114 };
    int head = 50;
  
    FCFS(arr, head);
}
}
  
// This code is contributed by 29AjayKumar

Python3

# Python program to demonstrate
# FCFS Disk Scheduling algorithm
  
size = 8;
  
def FCFS(arr, head):
  
    seek_count = 0;
    distance, cur_track = 0, 0;
  
    for i in range(size):
        cur_track = arr[i];
  
        # calculate absolute distance
        distance = abs(cur_track - head);
  
        # increase the total count
        seek_count += distance;
  
        # accessed track is now new head
        head = cur_track;
      
    print("Total number of seek operations = ", 
                                   seek_count);
  
    # Seek sequence would be the same
    # as request array sequence
    print("Seek Sequence is");
  
    for i in range(size):
        print(arr[i]);
      
# Driver code
if __name__ == '__main__':
  
    # request array
    arr = [ 176, 79, 34, 60,
            92, 11, 41, 114 ];
    head = 50;
  
    FCFS(arr, head);
  
# This code contributed by Rajput-Ji

C#

// C# program to demonstrate
// FCFS Disk Scheduling algorithm
using System;
  
class GFG
{
static int size = 8;
  
static void FCFS(int []arr, int head)
{
    int seek_count = 0;
    int distance, cur_track;
  
    for (int i = 0; i < size; i++) 
    {
        cur_track = arr[i];
  
        // calculate absolute distance
        distance = Math.Abs(cur_track - head);
  
        // increase the total count
        seek_count += distance;
  
        // accessed track is now new head
        head = cur_track;
    }
  
    Console.WriteLine("Total number of " + 
                    "seek operations = " + 
                              seek_count);
  
    // Seek sequence would be the same
    // as request array sequence
    Console.WriteLine("Seek Sequence is");
  
    for (int i = 0; i < size; i++)
    {
        Console.WriteLine(arr[i]);
    }
}
  
// Driver code
public static void Main(String[] args) 
{
    // request array
    int []arr = { 176, 79, 34, 60, 
                  92, 11, 41, 114 };
    int head = 50;
  
    FCFS(arr, head);
}
}
  
// This code is contributed by PrinciRaj1992

输出：

Total number of seek operations = 510
Seek Sequence is
176
79
34
60
92
11
41
114