C语言磁盘调度算法

C语言磁盘调度算法
1.FCFS（先来先服务）算法：
FCFS算法按照磁盘请求的顺序进行调度，即按照先来先服务的原则，先处理先到达磁盘的请求。

它的实现非常简单，只需要按照请求的顺序进
行访问即可。

C代码示例：
```c
#include <stdio.h>
#include <stdlib.h>
int fcfs(int start, int *requests, int n)
int i;
int total = abs(start - requests[0]);
for (i = 1; i < n; i++)
total += abs(requests[i] - requests[i - 1]);
}
return total;
int mai
int start = 50;
int requests[] = { 82,170, 43, 140, 24, 16, 190};
int n = sizeof(requests) / sizeof(requests[0]);
int total = fcfs(start, requests, n);
printf("Total head movement: %d\n", total);
return 0;
```
2.SSTF（最短寻道时间优先）算法：
SSTF算法每次都选择离当前磁道最近的请求进行处理，以减少寻道时间。

具体实现时，需要计算每个请求到当前磁道的距离，并选择最小的距离进行处理。

C代码示例：
```c
#include <stdio.h>
#include <stdlib.h>
int sstf(int start, int *requests, int n)
int i, j;
int total = 0;
int visited[n];
for (i = 0; i < n; i++)
visited[i] = 0;
}
int cur = start;
for (i = 0; i < n; i++)
int minDist = __INT_MAX__;
int index = -1;
for (j = 0; j < n; j++)
if (!visited[j])
int dist = abs(cur - requests[j]); if (dist < minDist)
minDist = dist;
index = j;
}
}
}
total += minDist;
visited[index] = 1;
cur = requests[index];
}
return total;
int mai
int start = 50;
int requests[] = { 82,170, 43, 140, 24, 16, 190};
int n = sizeof(requests) / sizeof(requests[0]);
int total = sstf(start, requests, n);
printf("Total head movement: %d\n", total);
return 0;
```
3.SCAN（电梯算法）算法：
SCAN算法模拟电梯的运行方式，先向一个方向扫描直到末尾，然后再改变方向向另一个方向扫描，以此往复。

具体实现时，需要记录当前扫描的方向，并按照该方向进行磁道的访问。

C代码示例：
```c
#include <stdio.h>
#include <stdlib.h>
int scan(int start, int *requests, int n)
int i, j;
int total = 0;
int direction = 1;
int cur = start;
for (i = 0; i < n; i++)
int minDist = __INT_MAX__;
int index = -1;
for (j = 0; j < n; j++)
if (requests[j] != -1)
int dist = abs(cur - requests[j]); if (dist < minDist)
minDist = dist;
index = j;
}
}
}
if (index == -1)
direction = -direction;
continue;
}
total += minDist;
cur = requests[index];
requests[index] = -1;
if (cur == 0 ， cur == 199)
direction = -direction;
}
cur = cur + direction;
}
return total;
int mai
int start = 50;
int requests[] = { 82,170, 43, 140, 24, 16, 190};
int n = sizeof(requests) / sizeof(requests[0]);
int total = scan(start, requests, n);
printf("Total head movement: %d\n", total);
return 0;
```
4.C-SCAN（循环扫描）算法：
C-SCAN算法类似于SCAN算法，不同之处在于它在达到磁盘末尾后，不是直接返回到起点，而是返回磁盘的开始位置，再次继续扫描。

C代码示例：
```c
#include <stdio.h>
#include <stdlib.h>
int c_scan(int start, int *requests, int n) int i, j;
int total = 0;
int cur = start;
for (i = 0; i < n; i++)
int minDist = __INT_MAX__;
int index = -1;
for (j = 0; j < n; j++)
if (requests[j] != -1)
int dist = (cur - requests[j] + 200) % 200;
if (dist < minDist)
minDist = dist;
index = j;
}
}
}
if (index == -1)
cur = 0;
continue;
}
total += minDist;
cur = requests[index];
requests[index] = -1;
}
return total;
int mai
int start = 50;
int requests[] = { 82,170, 43, 140, 24, 16, 190}; int n = sizeof(requests) / sizeof(requests[0]); int total = c_scan(start, requests, n);
printf("Total head movement: %d\n", total); return 0;
```
以上就是四种常见的C语言磁盘调度算法的实现。

根据不同的磁盘访问情况，选择合适的磁盘调度算法可以提高磁盘访问效率，减少磁头的移动次数。