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<DIV class=Section1>
<P class=MsoTitle><A name=_Toc534120514>Write Your Own Operating System
Tutorial</A></P>
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<H1>Lesson 1: The Boot Sector</H1>
<P class=MsoNormal>In this lesson well learn about the contents of the boot
sector so that we can learn to write our own boot program.</P>
<P class=MsoNormal>When the computer boots from a floppy, BIOS (Basic
Input/Output System) reads the disk and loads the first sector into memory at
address 0000:7C00.<SPAN style="mso-spacerun: yes"> </SPAN>This first
sector is called the DOS Boot Record (DBR).<SPAN
style="mso-spacerun: yes"> </SPAN>BIOS jumps to the address 0x7C00 and
begins executing instructions there.<SPAN style="mso-spacerun: yes">
</SPAN>It is these instructions (the boot loader) that will load the operating
system (OS) into memory and begin the OSs boot process.</P>
<P class=MsoNormal>The first thing to do is to take a look inside the Boot
Record.<SPAN style="mso-spacerun: yes"> </SPAN>The DOS utility DEBUG is a
widely available tool that can be used to view the contents of memory and
disks.<SPAN style="mso-spacerun: yes"> </SPAN>Well use DEBUG to look at a
floppy disks Boot Record.</P>
<P class=MsoNormal>At a DOS (or Windows) command prompt type <SPAN
style="FONT-FAMILY: 'Courier New'">debug</SPAN>.<SPAN
style="mso-spacerun: yes"> </SPAN>This will leave you with just a hyphen
as a prompt.<SPAN style="mso-spacerun: yes"> </SPAN>If you enter letter
d as a command and press Enter, it will show you a portion of the contents of
RAM.<SPAN style="mso-spacerun: yes"> </SPAN>Typing the question mark as a
command will give you a list of all the available commands in DEBUG.<SPAN
style="mso-spacerun: yes"> </SPAN>(<I>Be very careful when using the DEBUG
utility.<SPAN style="mso-spacerun: yes"> </SPAN>This utility can be used
to overwrite data on any disk drive, possibly causing loss of data.)</I></P>
<P class=MsoNormal>Place a freshly formatted disk in the A: drive.<SPAN
style="mso-spacerun: yes"> </SPAN>To load the Boot Record off your floppy
disk, type the following command.</P>
<P class=MsoNormal><SPAN
DIY手册.rar （20个子文件） 
操作系统DIY手册 
BOOT12.ASM 13KB H.ASM 3KB eng_ver Write Your Own Operating System - Lesson 2.htm 16KB Write Your Own Operating System - Lesson 5.htm 10KB Write Your Own Operating System - Lesson 6.htm 18KB Write Your Own Operating System - Lesson 3.htm 12KB Write Your Own Operating System - Lesson 1.htm 26KB Write Your Own Operating System - Lesson 4.htm 15KB Write Your Own Operating System - Lesson 7.htm 16KB
操作系统DIY手册（第二课）.doc 30KB 1.bat 7B 操作系统DIY手册（第三课）.doc 29KB 操作系统DIY手册（第一课）.doc 39KB 操作系统DIY手册（第五课）.doc 26KB 操作系统DIY手册（第四课）.doc 29KB 操作系统DIY手册（第六课）.doc 32KB
nasmw.exe 317KB LESSON6.ASM 1KB LESSON5.ASM 3KB HELOWRLD.ASM 3KB资源评论
