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FW,e HUV ;.HUV 3Ge HUV ;05+HUV 22l H$ ;1H$ 5Ge H$ ;33H$ 44l HHˆ;4HHˆY++7  ` Homework #3  `4Due Date:  Monday, February 21, 2000 at 11:59PM >`)Points:  80 regular, 10 extra credit O`Short-Answer Questions a`\These can be answered in a sentence or two, and are intended to reinforce important points. ms ~( 6 points ) Are disk scheduling policies other than first come, first serve (FCFS) useful when at most one user at a yr@Utime will be using the computer? Give a one-sentence justification for your answer. 1D= ( 6 points ) In section 2.2.4 of the text, a situation with a high-priority process,  H , and a low-priority process  L  0D<xwas described, which led to  H  looping forever. Does the same problem occur if round robin scheduling is used @Prather than priority scheduling? Why or why not? (text, chapter 2, problem 12) 2 }( 6 points ) Of the policies we have discussed in class, which requires the least amount of overhead time (the time @Bneeded to compute which process runs next)? Justify your answer. 0Z`Long-Answer Questions 3 tThese questions require some thought and longer answers than the short-answer questions. They are intended to have @`you use the concepts discussed in class, to be sure you understand them and can work with them. 5 ( 25 points ) Measurements of a certain system have shown that the average process runs for a time  T  before 0blocking on I/O. A process switch requires a time  S , which is effectively wasted ( i.e. , it is overhead time). For @{round robin scheduling with a quantum  Q , give a formula for the processor utilization for each of the following: 9*` Q  = :**`Q  >  T =`S  <  Q  <  T A`Q  =  S B`Q  nearly 0 C]*`(text, chapter 2, problem 21) 6iw]`o( 12 points ) In section 2.6.8, Tanenbaum writes that MINIX uses a multilevel scheduling algorithm 7 hIs the MINIX processor scheduling algorithm a multilevel feedback queue algorithm? If not, what distin'@"guishes it from a MLFQ algorithm? !8 vAre the quanta fixed  within  each level, or do they vary on a per-process basis? If they are fixed, are the oquanta fixed between levels, or does each level have a different quantum? If not, does the calculation of the @[quanta depend on the level of the process? Why do you think Tanenbaum made these choices? 4`K( 25 points ) Disk requests come into the disk drive for cylinders ;`#23 89 132 42 187 165 21 34 101 102 <] in that order. A seek takes 0.5 + 0.4 T  msec, where  T  is the number of cylinders moved. Calculate the mean and 0]rvariance of the waiting time for each of the following disk scheduling policies, assuming the arm is initially at @Hcylinder 100, the disk has 200 cylinders, and the arm is moving inward: @`first come, first serve (FCFS) M`shortest seek time next (SSTF) N`SCAN O`LOOK P`C-SCAN ?:` Extra Credit J] v( 10 points ) After receiving a DEL (SIGINT) character, the MINIX device driver discards all output currently PV]@>queued for that terminal. Why? (text, chapter 3, problem 30) HHˆ;6HHˆ66 l}?H A!9?H  GWHe- }H A8H  GWIe }? AKG?  HWJe d;;<@H$ ;<;>H$ == l H$ ;=;H$ <Wl8February 8, 2000ECS 150 Winter 2000Page 1  HUV ;>;<@HUV ?? l HUV ;?;HUV >WlDLast modified at  10:23 pm on Wednesday, February 9, 2000  HHˆ;@;>HHˆAA l HHˆ;A;HHˆ@W` }?H =x1C?H  FW-e¢ }H =zBOH  FW.a d=~EEd=Dd FF l d=Dd  tEtoje`[vCFILORU X[^adgjmpsy|  %).1OLI:!}?H A:H?H  HWKe-- }H BG!H  HWLe }? BNJ?  IWQe }?H BIK?H  IWRe° }H BJ:H  IWSe }? B QM?  JWTe }?H B LN?H  JWUe® }H B MIH  JWVe }? BCP?  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