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<title>Operating Systems: Partition Tables</title><body BGCOLOR=#FFFFFF TEXT=#000000><center><font face=Verdana size=7><b>Partition Tables</b></font></center><HR><p>This article is about the partitioning scheme that MS-DOS uses to keep trackof it's partitions. This is the standard that all PC operation systems mustuse to be allowed to share hard disk resources with other operating systems.<p>Send me any questions, comments, or corrections. <i><a href="mailto:sabre@nondot.org">Chris Lattner</a></i><p><HR Align=Center Width=400><br>DOS keeps track of partitions with a "Master Partition Table" that it keepsat offset 1BEh in the disk's boot sector. It contains four 16 byte entries, one for each partition. Each entry is divided into ten fields thatcontain all of the information necessary to describe a partition on thehard drive, including: <p><ul><li>Whether this partition is the one that got booted from.<br><li>The Head, Sector, and Cylinder where the partition starts.<br><li>The Head, Sector, and Cylinder where the partition ends.<br><li>The operating system that owns it.<br><li>The number of sectors that are before this partition.<br><li>The length of the partition in sectors.<br></ul>See: <strong><a href="#Fig_1">Figure 1</a></strong><p>Now the astute reader may say: "Wait a minute! On my machine I run DOS/Windowsand OS/2. I have 5 DOS partitions. How can this be!"<p>Microsoft's solution to this problem was to invent the "Extended DOS" partition. If you go into FDISK, you will see that you have a "Primary" DOSpartition, and an "Extended" DOS partition (Plus whatever else you have).You can also type in "UNFORMAT /PARTN /L" to get a list of all of your partitions.This clearly shows the chain format used. <p><H2><HR Align=Center Width=400><A NAME="Fig_1">Figure 1</H2><CENTER><TABLE BORDER CellPadding=10 WIDTH="50%"><TR ALIGN=CENTER> <TD></TD><TD ColSpan=3> Start </TD><TD></TD><TD ColSpan=3> End </TD></TR><TR ALIGN=CENTER> <TD>BI</TD> <TD>H</TD><TD>S</TD><TD>C</TD> <TD>SI</TD> <TD>H</TD><TD>S</TD><TD>C</TD> <TD ColSpan=4>SB</TD><TD ColSpan=4>NS</TD></TR><TR ALIGN=CENTER> <TD>0h</TD><TD>1h</TD><TD>2h</TD><TD>3h</TD><TD>4h</TD><TD>5h</TD><TD>6h</TD><TD>7h</TD> <TD>8h</TD><TD>9h</TD><TD>Ah</TD><TD>Bh</TD><TD>Ch</TD><TD>Dh</TD><TD>Eh</TD><TD>Fh</TD></TR></TABLE></CENTER><p>This is repeated four times (one for each partition). Offsets are:1BEh, 1CEh, 1DEh, and 1EEh. At offset 1FEh, AA55h signifies that the diskis bootable. The BIOS reads it in and executes it. See my article on <strong><a href="http://www.nondot.org/sabre/os/files/Booting/BootSector.html">Boot Sectors</a></strong>.<br><h3>Key:</H3><ul> BI: Boot indication. 0 = Not booted from. 80h = Booted from. <br> H: Head. Starting/Ending head number for the partition. <br> S: Sector. Starting/Ending sector number for the partition. This field also holds bits 8 and 9 of the cylinder in standard DOS format. <br> C: Cylinder. Lower 8 bits of the Starting/Ending cylinder number for the partition. <br> SI: System Indicator: <ul> 00h = Unused <br> 01h = DOS 12 bit FAT (0 - 16 megs) <br> 02h = XENIX root file system <br> 03h = XENIX /usr file system (obsolete) <br> 04h = DOS 16 bit FAT (16 - 32 megs) <br> 05h = Extended DOS partition <br> 06h = DOS 16 bit FAT (32 megs and up) <br> 07h = OS/2 High Performance File System <br> 07h = Windows NT (NTFS) <br> 07h = Advanced Unix <br> 0Ah = OS/2 Boot Manager <br> <li>For more, consult Ralf Brown's Interrupt list: INT 19 <br> </ul> SB (DWORD): Number of sectors before this partition. <br> NS (DWORD): Number of sectors in this partition. <br></ul><p><hr><FONT SIZE=4><TABLE ALIGN=RIGHT BORDER=0><TR><TD><center>Copyright © 1994-8 <i><a href="mailto:sabre@nondot.org">Chris Lattner</a></i><br>Last modified: Monday, 21-May-2001 13:25:25 CDT </center></TD></TR></TABLE>⌨️ 快捷键说明
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