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This paper selects two exercises from Operating System Concepts chapterfour and answers them providing justification and citations This paperwill cover the relationship between concurrency and parallelism thendiscuss Amdahls law and the speedup gains calculated with itThe first exercise that will be discussed is 411 Is it possible tohave concurrency but not parallelism Explain Concurrency is Acondition that exists when at least two threads are making progress Amore generalized form of parallelism that can include time-slicing as aform of virtual parallelism Oracle 2001 In contrast thedefinition of parallelism is A condition that arises when at least twothreads are executing simultaneously Oracle 2001 It is possiblefor two threads to make progress though not at the same instant As anexample consider a single-core processor running two threads Anoperating system will normally switch back and forth between the twothreads very quickly giving the appearance of parallelism However asseen in figure 1 the two threads are each taking turns executing theirrespective instructions on the same cpu core Though it is not possibleto have parallelism without concurrency it is possible to haveconcurrency but not parallelism Figure 1 Concurrent execution on a single-core system SilberschatzGalvin Gagne 2013The second exercise that will be discussed is 412 Using AmdahlsLaw calculate the speedup gain of an application that has a 60 percentparallel component for a two processing cores and b four processingcores Amdahls law states that the speedup from adding additionalcores will be less than or equal to 1 S 1-SN where S is thepart of a program that is preformed serially and N is the number ofprocessing cores Our task indicates an application has a 60 percentparallel component implying that it has a 40 percent serial componentseeing as 100 - 60 40 Therefore let S equal 040 For part a weare to assume two processing cores therefore let N 2 The speedupwill equal or be less than 10401-0402 This simplifies 107or approximately 143 For part b we are to assume
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