📄 booting-loading_process_5.htm
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<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN lang=EN-US><FONT
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Processing</STRONG></SPAN></FONT></SPAN></P><SPAN lang=EN-US><FONT
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<P><FONT size=4><SPAN lang=EN-US><FONT face="Times New Roman TUR"><SPAN
style="mso-tab-count: 1"><STRONG> <SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><FONT face="Times New Roman" size=5>1.5.1
Overview</FONT></SPAN></SPAN></STRONG></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt 21pt; TEXT-INDENT: -21pt; tab-stops: list 21.0pt; mso-list: l5 level1 lfo3"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
face="Times New Roman TUR" size=3>我们在After
Power-On一节已经介绍——当主机被启动之后，会自动将软盘或硬盘的第一个扇区的内容（<STRONG>boot block </STRONG>for
floppy, <STRONG>master boot </STRONG>for hard
disk）Load到内存0000:7c00H的位置，然后执行它。但OS的内核绝对不仅仅只有一个扇区大小。这就意味着boot
block需要进一步的从磁盘（软盘或硬盘）上读取OS的剩余部分。</FONT></SPAN></SPAN></SPAN></SPAN></SPAN></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt 21pt; TEXT-INDENT: -21pt; tab-stops: list 21.0pt; mso-list: l5 level1 lfo3"><SPAN
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lang=EN-US><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
size=3></FONT></SPAN></SPAN></SPAN></SPAN></SPAN> </P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt 21pt; TEXT-INDENT: -21pt; tab-stops: list 21.0pt; mso-list: l5 level1 lfo3"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
face="Times New Roman TUR"
size=3>事实上，从机器被Power-On或Reset之后，到OS的Kernel被正式的载入到运行，中间可以经历这些过程：</FONT></SPAN></SPAN></SPAN></SPAN></SPAN></P><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">
<OL type=1 start=0>
<LI><FONT face="Times New Roman TUR" size=3>由BIOS INT 19中断读入Master
boot；</FONT>
<LI></SPAN></SPAN></SPAN></SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
face="Times New Roman TUR" size=3>由Master boot读入并执行Boot
Block；</FONT></SPAN></SPAN></SPAN></SPAN></SPAN>
<LI><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"></SPAN></SPAN></SPAN></SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
face="Times New Roman TUR"><FONT size=3><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">由Master
boot读入并执行</SPAN></SPAN></SPAN></SPAN></SPAN>Second Booter（Monitor
or Setup Program)；</FONT></FONT></SPAN></SPAN></SPAN></SPAN></SPAN>
<LI><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"></SPAN></SPAN></SPAN></SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><FONT
face="Times New Roman TUR" size=3>最后由Second booter读入并执行OS
Kernel。</FONT></SPAN></SPAN></SPAN></SPAN></SPAN></LI></OL>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt 21pt; TEXT-INDENT: -21pt; tab-stops: list 21.0pt; mso-list: l5 level1 lfo3"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><FONT face="Times New Roman TUR"
size=3>比如Linux的启动过程为：</FONT></SPAN></SPAN></P><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><FONT face="Times New Roman TUR" size=3>
<OL type=1 start=0>
<LI>Master boot(LILO)
<LI></FONT></SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><FONT face="Times New Roman TUR" size=3>Boot
Block(bootsect.S)</FONT></SPAN></SPAN>
<LI><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US></SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><FONT face="Times New Roman TUR"
size=3>Setup(Setup.S)</FONT></SPAN></SPAN>
<LI><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US></SPAN></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><FONT face="Times New Roman TUR" size=3>Linux
Kernel</FONT></SPAN></SPAN></LI></OL>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt 21pt; TEXT-INDENT: -21pt; tab-stops: list 21.0pt; mso-list: l5 level1 lfo3"><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US><FONT face="Times New Roman TUR" size=3>Loading
Processing是Booting阶段的一个重要任务。为了很好的完成这一任务，我们必须清楚的了解磁盘（硬盘和软盘）操作的详细细节，对Loading过程和各个部分内存布局进行详细的规划。</FONT></SPAN></SPAN></P><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><SPAN
lang=EN-US>
<P>
<HR width="100%" SIZE=2>
<P></P>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt 21pt; TEXT-INDENT: -21pt; tab-stops: list 21.0pt; mso-list: l5 level1 lfo3"> <SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'"><STRONG><FONT
face="Times New Roman TUR" size=5>1.5.2 Memory Layout </FONT></STRONG></P>
<P><FONT face="Times New Roman TUR" size=3>在Real mode下，磁盘操作可以通过两种方法进行，BIOS
13H中断，或者通过读写端口。而在Protected
Mode下，BIOS中断不可用，只能通过读写端口的方式。而BIOS中断简单易用而且功能强大，同时我们在Booting阶段除了Loading
Processing之外，所作的许多工作都需要依赖BIOS中断，所以我们Loading Processing应该发生在Real
Mode下，通过BIOS中断调用来完成。</FONT></P>
<P><FONT face="Times New Roman TUR" size=3>但Real
Mode下的一种重要限制是1MB内存的局限，事实上仅有不到640
KB的可用RAM，我们必须把启动阶段所需要的各个程序，以及在启动阶段获取到的各种硬件参数，以及OS Kernel放入到这不到640
KB的RAM中。这样一来，我们如何在整个Booting阶段，合理有效的安排内存布局就显得非常重要。</FONT></P></SPAN></SPAN></SPAN>
<P class=MsoNormal
style="MARGIN: 0cm 0cm 0pt 21pt; TEXT-INDENT: -21pt; tab-stops: list 21.0pt; mso-list: l5 level1 lfo3"
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style="MARGIN: 0cm 0cm 0pt 21pt; TEXT-INDENT: -21pt; tab-stops: list 21.0pt; mso-list: l5 level1 lfo3"
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