MC415 - Operating System Final Exam Questions and Solution

1. What is interrupt An interrupt is a signal to the processor emitted by the hardware or software indicating an event needs immediate attention. 2. How does software trigger an interrupt? Software triggers an interrupt by executing a special operation called system call. . With the aid of a neat diagram! explain the role of an interrupt in a context switch.

". A process is a program in execution. With an aid of a neat diagram show the time relation between each of the # states a process can be in.

#. $xplain the function of the %rocess &ontrol 'loc( )%&'*.  +he function of the %&' is for for storing the the collection of of information information about the processes. %'& is a data structure in the operating system ,ernel containing the information needed to manage a particular process.

-. perating System theory distinguishes between threads and process. $xplain the di/erence between threads and processes.  +hreads are used for lightweight tas( whereas processes are used for more heavyweight tas(s.  +hreads within the same process share the same address space! whereas di/erent processes do not. •

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0. iscuss the three benets of multithreaded programming. 3ultithreading enables multitas(ing within a process  +hreads share the memory and the resources of the process to which they belong 3ultiple threads can run in parallel on di/erent processor. • •

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4. With the aid of a diagram! explain how a web server might use thread to advantage.

$very re5uest to the server can be met with a separate thread. 6. 7ace &ondition 7ace condition occurs when two or more threads can access shared data and try to change it at the same time. 18.$xplain the function of the software algorithm (nown as the %eterson Solution %eterson9s Algorithm uses a two process approach to solve the &S problem.  +he load and store processes. +wo variables share two processes: int turn; Boolean fag [2];  +he variable turn indicates whose turn it is to enter the critical section )&S*.  +he fag array is used to indicate if a process is ready to enter the critical section. •

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i.e. fag[i] = true implies the process

 Pi

 is ready.

11.What is the readers and writers9 problem and how is it overcome?  +he readers and writers9 problem is that;

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3ultiple readers are allowed to access
 +his problem is solved by (ernel providing read=write loc(s. nce the reader enters the entry section! it loc(s the resource. %reventing from writers. Subse5uent reader will access the loc(ed resource. +he last reader will unloc( the resource to available for writers. 12.$xplain the problem that can arise in the ining %hilosophers %roblem when there is no process synchroni>ation? ive philosopher sitting at a round dining table to eat. $ach philosopher has got a plate and one chopstic( at the right side of each plate. @n order to start eating! each of them need a plate and two chopstic(s. +hus! clearly there will be a deadloc( and starvation because of the limited number of chopstic(s. 1.ene the six )#* scheduling criteria to measure best performance. CPU Utilization  (eep the &%B as busy as possible. Throughput   number of processes completed their execution per time unit. Turnaround time  amount of time to execute a particular process. Waiting time  amount of time a process waits in the ready 5ueue. esponse time  amount of time it ta(es from when a re5uest was submitted until the rst response is produced. • •

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1".Show an SC scheduling chart using the following burst time.

a* +he Shortest Cob irst )SC* scheduling chart

b* &alculate the average waiting time for the SC data in part )a*.

( 3 + 16 + 9 + 0 ) 4

28 =

4

= 7  Milliseconds

c* What is the purpose of deterministic modeling?  +a(es a particular predetermined wor(load and denes the performance of  each algorithm for that wor(load.