![Quiz
1. The operating system can improve average disk
service time by scheduling the requests for disk
access [T/F]
TRUE
2. The time required to transfer of data between the
disk and main memory is called
TRANSFER TIME
http://raj-os.blogspot.in/ 19](https://image.slidesharecdn.com/diskscheduling-49-130319070336-phpapp01/85/Disk-scheduling-49-19-320.jpg)
![Quiz
3. If the desired disk drive and controller are available
the service can be serviced immediately [T/F]
TRUE
4. The disk scheduling algorithms are based on criteria
Minimize seek time
http://raj-os.blogspot.in/ 20](https://image.slidesharecdn.com/diskscheduling-49-130319070336-phpapp01/85/Disk-scheduling-49-20-320.jpg)
![Quiz
1. The FCFS algorithm does not provide best (average)
access [T/F]
TRUE
2. The head movement in the FCFS algorithm is
minimal in all cases [T/F]
FALSE
http://raj-os.blogspot.in/ 21](https://image.slidesharecdn.com/diskscheduling-49-130319070336-phpapp01/85/Disk-scheduling-49-21-320.jpg)
Disk scheduling.49
- 1. Disk Scheduling , FCFS disk scheduling algorithms http://raj-os.blogspot.in/ 1
- 2. HOME PREVIOUS TOPIC NEXT PREVIOUS QUESTION PAPERS FOR OS CPP TUTORIALS http://raj-os.blogspot.in/ 2
- 3. Recap In the last class, you have learnt: Various allocation methods - Their advantages and disadvantages http://raj-os.blogspot.in/ 3
- 4. Objectives On Completion of this period, you would be able to know • The Need for Disk Scheduling • FCFS disk scheduling algorithm http://raj-os.blogspot.in/ 4
- 5. Need for Disk Scheduling • Most jobs depend heavily on disk • It is important that disk service be as fast as possible for – Loading – Input – Output of files http://raj-os.blogspot.in/ 5
- 6. Need for Disk Scheduling • The operating system can improve average disk service time – By scheduling the requests for disk access http://raj-os.blogspot.in/ 6
- 7. Need for Disk Scheduling • Disk speed is composed of three parts • First – To access a block the system must move the head to the appropriate track or cylinder http://raj-os.blogspot.in/ 7
- 8. Need for Disk Scheduling • This head movement is called a SEEK • The time to complete it is SEEK TIME http://raj-os.blogspot.in/ 8
- 9. Need for Disk Scheduling • Once the head is at the right track – It must wait until the desired block rotates under read write head • This operation is called LATENCY(ROTATIOAL) • The delay is called LATENCY TIME http://raj-os.blogspot.in/ 9
- 10. Need for Disk Scheduling • The Transfer Time – The time required to transfer of data between the disk and main memory • The total time to service a disk request is the sum of – Seek time – Latency (rotational) time & – Transfer time http://raj-os.blogspot.in/ 10
- 11. Need for Disk Scheduling • The disk bandwidth is the ratio of The total number of bytes transferred The time between the first request of service and completion of transfer http://raj-os.blogspot.in/ 11
- 12. Disk Scheduling • Whenever a process needs a I/O from the disk – It issues a system call to the OS • The request has several pieces of information http://raj-os.blogspot.in/ 12
- 13. Disk Scheduling • Whether this operation is input or output • What the disk address for the transfer is • What is the memory address for the transfer • What the number of sectors to be transferred http://raj-os.blogspot.in/ 13
- 14. Disk Scheduling • If the desired disk drive and controller are available – The service can be serviced immediately • If the drive controller is busy – Any new requests will be placed in the queue http://raj-os.blogspot.in/ 14
- 15. Disk Scheduling • Multiprogramming system with many process • The disk queue may often have several pending requests • Thus when one request is completed • The operating system chooses which pending request is to service next http://raj-os.blogspot.in/ 15
- 16. Disk Scheduling • How does operating system makes this choice – Any of the disk scheduling algorithms can be used • We shall discuss various disk scheduling algorithms http://raj-os.blogspot.in/ 16
- 17. Various Disk Scheduling • FCFS Scheduling • SSTF Scheduling • SCAN Scheduling • C-SCAN Scheduling • LOOK Scheduling • C-LOOK Scheduling http://raj-os.blogspot.in/ 17
- 18. Disk Scheduling • All these algorithms are based on criteria i.e. – Minimize seek time • Seek time ≈ Seek distance http://raj-os.blogspot.in/ 18
- 19. Quiz 1. The operating system can improve average disk service time by scheduling the requests for disk access [T/F] TRUE 2. The time required to transfer of data between the disk and main memory is called TRANSFER TIME http://raj-os.blogspot.in/ 19
- 20. Quiz 3. If the desired disk drive and controller are available the service can be serviced immediately [T/F] TRUE 4. The disk scheduling algorithms are based on criteria Minimize seek time http://raj-os.blogspot.in/ 20
- 21. Quiz 1. The FCFS algorithm does not provide best (average) access [T/F] TRUE 2. The head movement in the FCFS algorithm is minimal in all cases [T/F] FALSE http://raj-os.blogspot.in/ 21
- 22. Other subject materials • Web designing • Micro processors • C++ tutorials • java home http://raj-os.blogspot.in/ 22