📄 fat文件系统原理(二).htm
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<TD class=title_maintxt vAlign=center width="82%"> <IMG
height=14 src="FAT文件系统原理(二).files/arrow.gif" width=11
align=absMiddle> FAT文件系统原理(二) </TD>
<TD class=title_maintxt width="18%"> <FONT
color=red>热</FONT> <FONT
color=#009900>★★★</FONT> </TD></TR></TBODY></TABLE></TD></TR>
<TR vAlign=center align=middle>
<TD colSpan=2 height=40><FONT
size=4><STRONG>FAT文件系统原理(二)</STRONG></FONT> </TD></TR>
<TR class=tdbg_rightall align=middle>
<TD colSpan=2>［ 作者：<A
href="mailto:zymail@vip.sina.com">菜刀</A> 转贴自：本站原创 点击数：546 更新时间：2004-4-20 文章录入：admin
］</TD></TR>
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<P>
<P>
<P>四、FAT分区原理。</P>
<P>先来一幅结构图：<BR> <IMG height=640
src="FAT文件系统原理(二).files/2004420123411734.gif" width=322
border=0><BR><FONT color=#c0c0c0><SPAN
style="FONT-WEIGHT: 700; BACKGROUND-COLOR: #ffff00"><BR></SPAN></FONT>
现在我们着重研究FAT格式分区内数据是如何存储的。FAT分区格式是MICROSOFT最早支持的分区格式，依据FAT表中每个簇链的所占位数(有关概念，后面会讲到)分为fat12、fat16、fat32三种格式"变种"，但其基本存储方式是相似的。<BR>
仔细研究图7中的fat16和fat32分区的组成结构。下面依次解释DBR、FAT1、FAT2、根目录、数据区、剩余扇区的概念。提到的地址如无特别提示均为分区内部偏移。</P>
<P>4.1 关于DBR.</P>
<P> DBR区(DOS BOOT
RECORD)即操作系统引导记录区的意思，通常占用分区的第0扇区共512个字节(特殊情况也要占用其它保留扇区，我们先说第0扇)。在这512个字节中，其实又是由跳转指令，厂商标志和操作系统版本号，BPB(BIOS
Parameter Block)，扩展BPB，os引导程序，结束标志几部分组成。
以用的最多的FAT32为例说明分区DBR各字节的含义。见图8。<BR> <IMG
height=707 src="FAT文件系统原理(二).files/2004420123411580.gif"
width=569 border=0><BR><FONT color=#c0c0c0><SPAN
style="FONT-WEIGHT: 700; BACKGROUND-COLOR: #ffff00"></SPAN></FONT><BR>图8的对应解释见表3
</P>
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<TD align=middle colSpan=4><FONT
size=3> </FONT><FONT
size=3>表3
FAT32分区上DBR中各部分的位置划分 </FONT></TD></TR>
<TR>
<TD align=middle width="14%"><FONT size=3>字节位移</FONT></TD>
<TD align=middle width="30%"><FONT size=3>字段长度</FONT></TD>
<TD align=middle width="25%"><FONT size=3>字段名</FONT></TD>
<TD align=middle width="7%"><FONT
size=3>对应图8颜色</FONT></TD></TR>
<TR>
<TD align=middle width="14%"><FONT size=3>0x00</FONT></TD>
<TD align=middle width="30%"><FONT size=3>3个字节</FONT></TD>
<TD align=middle width="25%"><FONT size=3>跳转指令</FONT></TD>
<TD align=middle width="7%" bgColor=#0000ff> </TD></TR>
<TR>
<TD align=middle width="14%"><FONT size=3>0x03</FONT></TD>
<TD align=middle width="30%"><FONT size=3>8个字节</FONT></TD>
<TD align=middle width="25%"><FONT
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