Skip to main content

Round-Robin Scheduling in operating system-computer world

 Round-Robin Scheduling in operating system-computer world

Round-Robin Scheduling 

The round-robin(R-R Scheduling) Scheduling algorithm is designed for time sharing operating system. Round-Robin is similar to FCFS Scheduling, but preemption is added to enable the system to switch between processes. In Round-Robin Scheduling a small unit of time is used which is called a time quantum or time slice. A time quantum is generally from 10 to 100 millisecond. The CPU Scheduler goes around the ready queue, allocate the CPU to every process for a time interval of up to 1 time quantum. In this scheduling new processes are added to the tail of the ready queue. The CPU scheduler picks the first process from ready queue, set a timer after one time slice and dispatch the process. One of two things will happens. When a process have CPU burst of less the 1 time quantum. In this case the process itself release the CPU. If the CPU burst time of the currently running process is longer then one time quantum, the will go off . A context will executed, and the process will be put at the tail of the ready queue. The CPU scheduler will the select the next process in the ready queue. The average waiting time under the R-R scheduling is long.  The performance of R-R scheduling is depends on the size the time quantum. In R-R scheduling algorithm, the operating system defines a time quantum. All the process will executed in the cyclic way each process will get the CPU for a small amount of time and then get back to the ready queue to wait for its next turn. The new process is added to the ready queue. Context switching is used to save the processes in PCB. Consider the following set of processes that arrive time 0, with the length of the CPU burst given in milliseconds.

Process                                    Burst Time

 P1                                                             24

 P3                                                              3

 P3                                                              3

In this case we use time quantum of 4 milliseconds, the process p1 gets the first 4 millisecond. Since it require another 20 milliseconds, it is permitted after the first time quantum, and the CPU is given to the next process ,process p2. Process p2 does not need 4 milliseconds, so it quits before it's time quantum expires. The CPU is given to the next process , process p3 once each process received 1 time quantum, the CPU return to the process p1. 

Let's calculate the average waiting time for this schedule. P1 wait for 6 millisecond (10-4), P2 wait for 4 millisecond, p3 wait for 7 millisecond. The average waiting time is 17/3 = 5.66 millisecond.



Comments

Post a Comment

Popular posts from this blog

Difference between HTML and DHTML-computer world

     Difference between HTML and DHTML  HTML is a markup language, while DHTML is a collection of Technology.  DHTML creates dynamic web page, whereas HTML create static web page.  DHTML allow including small animations and dynamic menus in web pages but HTML is not able to do so.   HTML used events, methods, properties to insulate dynamism in HTML pages.   HTML is used to describe the web page but DHTML is a collection of JavaScript and style sheet in an HTML page. HTML sites will be show upon client side Technologies, while  DHTML site will be fast enough upon client side Technologies as most of entries are checked on browser itself and not waste time rendering to server for mistake.  HTML creates a plain web page without any style and scripts called as HTML. Whereas,  DHTML creates a page with HTML, CSS,DOM And scripts called as DHTML.  HTML cannot any server side code but XHTML may contain server side code.  ...
Post a Comment
Read more

Aggregation and Functional dependency in DBMS-computer world

  Aggregation and  Functional dependency in  DBMS Aggregation  In aggregation the relation between two entities is treated as a single entity. In aggregation relationship with its corresponding entity is aggregated into higher level entity . It is the process of compiling information on object, there by obstructing a higher level. On limitation of the ER model is that it can not Express relationship among relationships. The aggregation represent a relationship between a whole object and its component in other word we can say that using aggregation we can express relationship main relationships.  For example center entity offer the course entity act as a single entity in the relationship which is in a relationship with another entity visitor. In the real world if a visitor visits a coaching center they will never inquiry about the course or just about the center instead he will ask the inquiry about both. Functional dependency  Functional dependency play an ...
Post a Comment
Read more

Nested relation -oocomputer world

 Nested relation   During the first normal form we require that all attributes have atomic domain a domain is atomic if elements of the domain are considered to be indivisible unit.  For example the set of integer is an atomic domain but the set of all sets of integer is a non atomic domain. We considered set of integer to have subpart the important issue in first normal form not the domain itself but rather the way we use domain element in database. The nested relational model is a extension of the relation model in which domain may be either atomic or relation  valued of a tuple on a attribute may be relation and relation may be stored within relation . A complex objects can be represented by a single tuple of a nested relation if we view a tuple of a nested relation a data item we have a one to one correspondence between data item and objects in the user's view of the database.  Nested relation are just one example of extensions to the basic relational m...
Post a Comment
Read more