Tag: FCFS Disk Scheduling

Disk Scheduling | Disk Scheduling Algorithms

Operating System

Disk Scheduling-

 

Before you go through this article, make sure that you have gone through the previous article on Magnetic Disk.

 

Disk scheduling is a technique used by the operating system to schedule multiple requests for accessing the disk.

 

Disk Scheduling Algorithms-

 

  • The algorithms used for disk scheduling are called as disk scheduling algorithms.
  • The purpose of disk scheduling algorithms is to reduce the total seek time.

 

Various disk scheduling algorithms are-

 

 

  1. FCFS Algorithm
  2. SSTF Algorithm
  3. SCAN Algorithm
  4. C-SCAN Algorithm
  5. LOOK Algorithm
  6. C-LOOK Algorithm

 

In this article, we will discuss about FCFS Disk Scheduling Algorithm.

 

FCFS Disk Scheduling Algorithm-

 

  • As the name suggests, this algorithm entertains requests in the order they arrive in the disk queue.
  • It is the simplest disk scheduling algorithm.

 

Advantages-

 

  • It is simple, easy to understand and implement.
  • It does not cause starvation to any request.

 

Disadvantages-

 

  • It results in increased total seek time.
  • It is inefficient.

 

PRACTICE PROBLEM BASED ON FCFS DISK SCHEDULING ALGORITHM-

 

Problem-

 

Consider a disk queue with requests for I/O to blocks on cylinders 98, 183, 41, 122, 14, 124, 65, 67. The FCFS scheduling algorithm is used. The head is initially at cylinder number 53. The cylinders are numbered from 0 to 199. The total head movement (in number of cylinders) incurred while servicing these requests is _______.

 

Solution-

 

 

Total head movements incurred while servicing these requests

= (98 – 53) + (183 – 98) + (183 – 41) + (122 – 41) + (122 – 14) + (124 – 14) + (124 – 65) + (67 – 65)

= 45 + 85 + 142 + 81 + 108 + 110 + 59 + 2

= 632

 

To gain better understanding about FCFS Disk Scheduling Algorithm,

Watch this Video Lecture

 

Next Article- SSTF Disk Scheduling Algorithm

 

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