OS-Disk Scheduling

In multiprogrammed computing systems, many processes may be generating requests for reading and writing disk records. Because these processe...

In multiprogrammed computing systems, many processes may be generating requests for reading and writing disk records. Because these processes sometimes make requests faster than they can be serviced by the moving-head disks, waiting lines or queues build up for each device. Some computing systems simply service these requests on a first-come-first-served (FCFS) basis. Whichever request for service arrives first is serviced first. FCFS is a fair method of allocating service, but when the request rate becomes heavy, FCFS can result in very long waiting times.

FCFS exhibits a random seek pattern in which successive requests can cause time consuming seeks from the innermost to the outermost cylinders. To minimize time spent seeking records, it seems reasonable to order the request queue in some manner other than FCFS. This process is called disk scheduling.



Disk scheduling involves a careful examination of pending requests to determine the most efficient way to service the requests.A disk scheduler examines the positional relationships among waiting requests. The request queue is then reordered so that the requests will be serviced with minimum mechanical motion. 
The two most common types of scheduling are seek optimization and rotation (or latency) optimization.



DESIRABLE CHARACTERISTICS OF DISK SCHEDULING POLICIES:

Several other criteria for categorizing scheduling policies are
  1.  throughput
  2.  mean response time
  3.  variance of response times (ie., predictability)
A scheduling policy should attempt to maximize throughput the number of requests serviced per unit time. A scheduling policy should attempt to minimize the mean response time (or average waiting time plus average service time). Variance is a mathematical measure of how far individual items tend to deviate from the average of the items. Variance to indicate predictability- the smaller the variance, the greater the predictability. We desire a scheduling policy that minimizes variance.
Name

ADO,131,ASP,3,C++,61,CORE JAVA,1,CSS,115,HTML,297,index,5,JAVASCRIPT,210,OS,47,PHP,65,SAD,53,SERVLETS,23,SOFTWARE ENGINEERING,245,SQL,71,TCP/IP,1,XHTML,9,XML,18,
ltr
item
Best Online Tutorials | Source codes | Programming Languages: OS-Disk Scheduling
OS-Disk Scheduling
http://2.bp.blogspot.com/-qfJWsT7eBeI/UC0KWASoGbI/AAAAAAAAAzw/xZNBFAffFvY/s400/Capture.PNG
http://2.bp.blogspot.com/-qfJWsT7eBeI/UC0KWASoGbI/AAAAAAAAAzw/xZNBFAffFvY/s72-c/Capture.PNG
Best Online Tutorials | Source codes | Programming Languages
https://www.1000sourcecodes.com/2012/09/os-disk-scheduling.html
https://www.1000sourcecodes.com/
https://www.1000sourcecodes.com/
https://www.1000sourcecodes.com/2012/09/os-disk-scheduling.html
true
357226456970214079
UTF-8
Loaded All Posts Not found any posts VIEW ALL Readmore Reply Cancel reply Delete By Home PAGES POSTS View All RECOMMENDED FOR YOU LABEL ARCHIVE SEARCH ALL POSTS Not found any post match with your request Back Home Sunday Monday Tuesday Wednesday Thursday Friday Saturday Sun Mon Tue Wed Thu Fri Sat January February March April May June July August September October November December Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec just now 1 minute ago $$1$$ minutes ago 1 hour ago $$1$$ hours ago Yesterday $$1$$ days ago $$1$$ weeks ago more than 5 weeks ago Followers Follow THIS PREMIUM CONTENT IS LOCKED STEP 1: Share to a social network STEP 2: Click the link on your social network Copy All Code Select All Code All codes were copied to your clipboard Can not copy the codes / texts, please press [CTRL]+[C] (or CMD+C with Mac) to copy Table of Content