FCFS和SSTF磁盘调度算法之间的区别

先决条件–磁盘调度算法
1. FCFS磁盘调度算法：
先到先服务，顾名思义，该算法按照它们到达磁盘队列的顺序来招待任务。它是最简单易懂的磁盘调度算法。在这种情况下，头部或指针沿任务到达的方向移动并移动，直到满足所有请求为止。 FCFS提供了更多的平均等待时间和响应时间。但是，FCFS算法具有处理即将到来的请求的更公平的策略。

例子：
考虑具有200个磁道(0-199)的磁盘和具有I / O请求的磁盘队列，其顺序如下：

98, 183, 40, 122, 10, 124, 65 

Read \ Write磁头的当前磁头位置为53。使用FCFS算法计算Read / Write磁头的磁道移动总数。

头部总动作

= (98-53)+(183-98)+(183-40)+(122-40)+(122-10)+(124-10)+(124-65)
= 640

2. SSTF磁盘调度算法：
SSTF代表最短查找时间优先，顾名思义，它服务于最接近头或指针当前位置的请求。在该算法中，头部指针的方向非常重要。如果不知何故，我们在请求之间遇到了障碍，那么负责人将在请求的持续方向上为其提供服务。与FCFS相比，SSTF算法在寻道时间上非常有效。

例子：
考虑具有200个磁道(0-199)的磁盘和具有I / O请求的磁盘队列，其顺序如下：

98, 183, 40, 122, 10, 124, 65 

Read \ Write磁头的当前磁头位置为53，它将向右移动。使用SSTF算法计算读/写磁头的磁道移动总数。

头部总动作

= (65-53)+(65-40)+(40-10)+(98-10)+(122-98)+(124-122)+(183-124)
= 240

FCFS和SSTF磁盘调度算法之间的区别：

	FCFS SCHEDULING ALGORITHM	SSTF SCHEDULING ALGORITHM
1.	FCFS is not efficient in seek movements.	SSTF is very effective/efficient in seek movements.
2.	It results in increased total seek time.	It reduces the total seek time as compared to FCFS.
3.	It provides more average waiting time and response time.	This algorithm provides less average response time and waiting time.
4.	In this algorithm direction of head does not matters much, which we can clearly see in above example.	But here direction of head plays an important role, in order to break tie between requests and above example is a proof of it.
5.	This algorithm is the easy to understand and implement.	Here, there is an overhead of finding out the closest request.
6.	FCFS does not cause starvation to any request (but may suffer from Convoy effect.).	Here, the request which are far from head will suffer starvation.
7.	In FCFS algorithm there is decrement in Throughput.	Here in SSTF there is increment in Throughput.