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在有一台处理机CPU和两台输入输出设备IO1和IO2,且能够实现抢先式多任务并行工作的多道程序内,投入运行优先级由高到低的P1,P2,P3三个作业。它们使用设备的先后顺序和占用设备时间分别是:

 作业P1:IO2(30毫秒)CPU(10毫秒)IO1(30毫秒)CPU(10毫秒)

 作业P2:IO1(20毫秒)CPU(20毫秒)IO2(40毫秒)

 作业P3:CPU(30毫秒)IO1(20毫秒)

在对于其他辅助操作时间可以忽略不计的假设下,作业P1,P2,P3从投入到完成所用的时间分别是(55)毫秒,(56)毫秒和(57)毫秒。三个作业从投入运行到全部完成,CPU的利用率约为(58)%,IO1的利用率约为(59)%。

假定在系统中仅有这三个作业投入运行,各设备的利用率是指该设备的使用时间同作业进程全部完成所占用最长时间的比率。

  • A.60
  • B.67
  • C.70
  • D.78
  • E.80
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