磁盘管理

1. Disk requests come in to the disk driver for cylinders 10, 22, 2, 40, and 38 in that order. The arm is initially at cylinder 20. Suppose a piece of seek takes 6ms per cylinder moved. Please compute seek time using:
   (a)FCFS (First come first served);
   (b)SSF (Shorted seek first);
   (c)ELEVATOR ALGORITHM (initially moving upward).
   Please draw the arm motion figure.

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磁盘请求按顺序进入磁盘驱动器10，22，2，40和38。 手臂最初是在柱面20上。假设一块寻道柱面移动花费6毫秒。 请使用以下方式计算搜索时间：
（a）FCFS（先来先服务）;
（b）SSF（最短寻道优先）;
（c）电梯算法（最初向上移动）。
请绘制手臂运动图。

Answer:
(a)
Seek time=(10+12+20+38+2)×6
=492ms

从20开始，按照题目所给顺序依次寻找就可以了

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(b)
Seek time=(2+12+8+36+2)×6
=360ms

从20开始，每次都找离当前位置最近的柱面

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(c)
Seek time=(2+16+2+30+8)×6
=348ms

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In which of the four I/O software layers is each of the following done.
(a)Computing the track,sector,and head for a disk read.
(b)Writing commands to the device registers.
(c)Checking to see if the user is permitted to use the device.
(d)Converting binary integers to ASCII for printing

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在四个I / O软件层中的哪一个是以下每个完成的。
（a）计算磁盘读取的轨道，扇区和磁头。
（b）向设备寄存器写入命令。
（c）检查用户是否被允许使用设备。
（d）将二进制整数转换为ASCII进行打印

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Solution:
(a) Device driver
(b) Device driver
(c) Device-independent IO software
(d) User-level IO software

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解：
（a）设备驱动程序
（b）设备驱动程序
（c）与设备无关的IO软件
（d）用户级IO软件