ch9.htm

汤子瀛《操作系统》电子教案

      </o:p>
      </span></font></p>
      <p><font color="#FFFFFF"><span style="mso-spacerun: yes; mso-bidi-font-size: 10.0pt" lang="EN-US">&nbsp;</span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">⑵最短寻道时间优先：</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
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      <p><font color="#FFFFFF"><span style="mso-spacerun: yes; mso-bidi-font-size: 10.0pt" lang="EN-US">&nbsp;&nbsp; 
      </span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">总是选择请求对列中距磁头当前距离最近的请求为之服务。</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p><font color="#FFFFFF"><span style="mso-spacerun: yes; mso-bidi-font-size: 10.0pt" lang="EN-US">&nbsp;&nbsp; 
      </span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">缺点：新请求不断到达，磁头往往滞留在中央柱面，致使远离中央的柱面的访问无限延长。“饿死”现象</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p><font color="#FFFFFF"><span style="mso-spacerun: yes; mso-bidi-font-size: 10.0pt" lang="EN-US">&nbsp;</span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">⑶各种扫描算法</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p style="MARGIN-LEFT: 21pt; TEXT-INDENT: -10.5pt; tab-stops: list 21.0pt; mso-list: l22 level1 lfo36"><font color="#FFFFFF"><span lang="EN-US" style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">①</span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">扫描算法（</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt">SCAN</span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">）：</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p style="MARGIN-LEFT: 21pt"><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">进程“饥饿”现象</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">　</span><span style="mso-spacerun: yes; mso-bidi-font-size: 10.0pt" lang="EN-US">&nbsp; 
      </span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">总是选择请求对列中沿移动臂移动方向上距磁头当前距离最近的请求为之服务。</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p><font color="#FFFFFF"><span style="mso-spacerun: yes; mso-bidi-font-size: 10.0pt" lang="EN-US">&nbsp; 
      </span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">②循环扫描算法（</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt">CSCAN</span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">）：</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">　③</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt">N-Step-SCAN</span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">调度算法</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><span style="mso-spacerun: yes">&nbsp;&nbsp;&nbsp;&nbsp; 
      </span>N-Step-SCAN</span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">调度算法</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p><font color="#FFFFFF"><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><span style="mso-spacerun: yes">&nbsp;&nbsp;&nbsp;&nbsp; 
      </span>FSCAN</span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">调度算法</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p><span lang="EN-US"><font color="#FFFFFF">&nbsp;<o:p>
      </o:p>
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    <p style="TEXT-ALIGN: center" align="center"><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><font color="#FFFFFF"><a name="ch92"></a>9．2<span style="mso-spacerun: yes">&nbsp; 
    </span>外存分配方法<o:p>
    </o:p>
    </font></span></p>
    <p style="MARGIN-LEFT: 18pt; TEXT-INDENT: -18pt; tab-stops: list 18.0pt; mso-list: l35 level1 lfo30"><font color="#FFFFFF"><span lang="EN-US" style="mso-fareast-font-family: 黑体">1．</span><span style="mso-ascii-font-family: Times New Roman">连续分配：</span><span lang="EN-US" style="mso-fareast-font-family: 黑体"><o:p>
    </o:p>
    </span></font></p>
    <p style="MARGIN-LEFT: 18pt"><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">优点：顺序访问容易；顺序访问速度快。</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
    </o:p>
    </span></font></p>
    <p style="MARGIN-LEFT: 18pt"><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">缺点：要求有连续的存储空间</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
    </o:p>
    </span></font></p>
    <p style="MARGIN-LEFT: 18pt"><font color="#FFFFFF"><span style="mso-spacerun: yes; mso-bidi-font-size: 10.0pt" lang="EN-US">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
    </span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">必须事先知道文件的长度</span></font></p>
    <p style="MARGIN-LEFT: 18pt; TEXT-INDENT: -18pt; tab-stops: list 18.0pt; mso-list: l35 level1 lfo30"><font color="#FFFFFF"><span lang="EN-US" style="mso-fareast-font-family: 黑体">2．</span><span style="mso-ascii-font-family: Times New Roman">链接分配</span><span lang="EN-US" style="mso-fareast-font-family: 黑体"><o:p>
    </o:p>
    </span></font></p>
    <p style="MARGIN-LEFT: 18pt"><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">隐式链接：在文件目录的每个目录项中含有指向链接文件第一和最后一个盘块的指针</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
    </o:p>
    </span></font></p>
    <p style="MARGIN-LEFT: 18pt"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><font color="#FFFFFF">显式链接：把用于链接文件各物理块的指针，显式的存放在内存的一张链接表中</font></span></p>
    <p style="MARGIN-LEFT: 18pt; TEXT-INDENT: -18pt; tab-stops: list 18.0pt; mso-list: l35 level1 lfo30"><font color="#FFFFFF"><span lang="EN-US" style="mso-fareast-font-family: 黑体">3．</span><span style="mso-ascii-font-family: Times New Roman">索引分配</span><span lang="EN-US" style="mso-fareast-font-family: 黑体"><o:p>
    </o:p>
    </span></font></p>
    <p style="MARGIN-LEFT: 18pt"><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">单级索引分配：</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
    </o:p>
    </span></font></p>
    <p style="MARGIN-LEFT: 18pt"><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">多级索引分配：</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
    </o:p>
    </span></font></p>
    <p style="MARGIN-LEFT: 18pt"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman"><font color="#FFFFFF">混合分配方式：直接地址、一次间接地址、多次间接地址</font></span></p>
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      <p style="TEXT-ALIGN: center" align="center"><font color="#FFFFFF"><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><a name="ch93"></a>9</span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">．</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt">3<span style="mso-spacerun: yes">&nbsp; 
      </span></span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">空闲存储空间的管理</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p style="MARGIN-LEFT: 18pt; TEXT-INDENT: -18pt; tab-stops: list 18.0pt; mso-list: l26 level1 lfo31"><font color="#FFFFFF"><span lang="EN-US" style="mso-fareast-font-family: 黑体">1．</span><span style="mso-ascii-font-family: Times New Roman">空闲表法：</span><span lang="EN-US" style="mso-fareast-font-family: 黑体"><o:p>
      </o:p>
      </span></font></p>
      <p style="MARGIN-LEFT: 18pt; TEXT-INDENT: -18pt; tab-stops: list 18.0pt; mso-list: l26 level1 lfo31"><font color="#FFFFFF"><span lang="EN-US" style="mso-fareast-font-family: 黑体">2．</span><span style="mso-ascii-font-family: Times New Roman">空闲链表法</span><span lang="EN-US" style="mso-fareast-font-family: 黑体"><o:p>
      </o:p>
      </span></font></p>
      <p><font color="#FFFFFF"><span style="mso-spacerun: yes" lang="EN-US">&nbsp;</span><span style="mso-spacerun: yes; mso-bidi-font-size: 10.0pt" lang="EN-US">&nbsp;</span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">⑴空闲盘块链</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p><font color="#FFFFFF"><span style="mso-spacerun: yes; mso-bidi-font-size: 10.0pt" lang="EN-US">&nbsp; 
      </span><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">⑵空闲盘区链</span></font></p>
      <p style="MARGIN-LEFT: 18pt; TEXT-INDENT: -18pt; tab-stops: list 18.0pt; mso-list: l26 level1 lfo31"><font color="#FFFFFF"><span lang="EN-US" style="mso-fareast-font-family: 黑体">3．</span><span style="mso-ascii-font-family: Times New Roman">位示图法</span><span lang="EN-US" style="mso-fareast-font-family: 黑体"><o:p>
      </o:p>
      </span></font></p>
      <p style="TEXT-INDENT: 18pt"><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">位示图</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p style="TEXT-INDENT: 18pt"><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">盘块的分配</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p style="TEXT-INDENT: 18pt"><font color="#FFFFFF"><span style="mso-bidi-font-size: 10.0pt; mso-ascii-font-family: Times New Roman; mso-hansi-font-family: Times New Roman">盘块的回收</span><span lang="EN-US" style="mso-bidi-font-size: 10.0pt"><o:p>
      </o:p>
      </span></font></p>
      <p style="MARGIN-LEFT: 18pt; TEXT-INDENT: -18pt; tab-stops: list 18.0pt; mso-list: l26 level1 lfo31"><font color="#FFFFFF"><span lang="EN-US" style="mso-fareast-font-family: 黑体">4．</span><span style="mso-ascii-font-family: Times New Roman">成组链接法</span><span lang="EN-US" style="mso-fareast-font-family: 黑体"><o:p>
      </o:p>
      </span></font></p>