244 lines
5.6 KiB
HTML
244 lines
5.6 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>How the DOS plug-in is implemented</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="EVMS User Guide"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="The DOS plug-in"
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HREF="appxdos.html"><LINK
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REL="PREVIOUS"
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TITLE="The DOS plug-in"
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HREF="appxdos.html"><LINK
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REL="NEXT"
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TITLE="Assigning the DOS plug-in"
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HREF="assigndos.html"></HEAD
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><BODY
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CLASS="sect1"
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BGCOLOR="#FFFFFF"
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SUMMARY="Header navigation table"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>EVMS User Guide</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Appendix A. The DOS plug-in</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="assigndos.html"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="sect1"
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><H1
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CLASS="sect1"
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><A
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NAME="DOShow"
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></A
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>A.1. How the DOS plug-in is implemented</H1
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><P
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>The DOS plug-in provides compatibility with DOS partition tables.
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The plug-in produces EVMS segment storage objects that map primary partitions
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described by the MBR partition table and logical partitions
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described by EBR partition tables.
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</P
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><P
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>DOS partitions have names that are constructed from two pieces
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of information:</P
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><P
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></P
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><UL
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><LI
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><P
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>The device they are found on.</P
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></LI
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><LI
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><P
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>The partition table entry that provided the information.</P
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></LI
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></UL
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><P
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>Take, for example, partition name <TT
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CLASS="filename"
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>hda1</TT
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>, which
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describes a partition that is found on device <TT
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CLASS="filename"
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>hda</TT
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>
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in the MBR partition table.
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DOS partition tables can hold four entries.
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Partition numbers 1-4 refer to MBR partition records. Therefore, our
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example is telling us that partition <TT
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CLASS="filename"
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>hda1</TT
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> is described
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by the very first partition record entry in the MBR partition table.
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Logical partitions, however, are different than primary partitions.
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EBR partition tables are scattered across a disk but are linked together
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in a chain that is first located using an extended partition record found
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in the MBR partition table.
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Each EBR partition table contains a partition record that describes a logical
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partition on the disk.
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The name of the logical partition reflects its position in the EBR chain.
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Because the MBR partition table reserves numerical names 1-4, the very
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first logical partition is always named 5.
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The next logical partition, found by following the EBR chain, is called 6,
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and so forth.
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So, the partition <TT
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CLASS="filename"
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>hda5</TT
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> is a logical partition that is
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described by a partition record in the very first EBR partition table.
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</P
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><P
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>While discovering DOS partitions, the DOS plug-in also looks for
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OS/2 DLAT metadata to further determine if the disk is an OS/2 disk.
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An OS/2 disk has additional metadata and the metadata is validated during
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recovery.
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This information is important for the DOS plug-in to know because an OS/2
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disk must maintain additional partition information. (This is why the
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DOS plug-in asks, when being assigned to a disk, if the disk is a
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Linux disk or an OS/2 disk.) The DOS plug-in needs to know how much
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information must be kept on the disk and what kind of questions it should
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ask the user when obtaining the information.
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</P
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><P
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> An OS/2 disk can contain compatibility volumes as well as logical volumes.
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A compatibility volume is a single partition with an assigned drive
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letter that can be mounted. An OS/2 logical volume is a drive link of 1
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or more partitions that have software bad-block relocation at the
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partition level.
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</P
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><P
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> Embedded partitions, like those found on a SolarisX86 disk or a BSD
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compatibility disk, are found within a primary partition.
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Therefore, the DOS plug-in inspects primary partitions that it has
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just discovered to further determine if any embedded partitions exist.
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Primary partitions that hold embedded partition tables have partition
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type fields that indicate this.
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For example, a primary partition of type 0xA9 probably has a BSD partition
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table that subdivides the primary partition into BSD partitions.
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The DOS plug-in looks for a BSD disk label and BSD data partitions in the
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primary partition.
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If the DOS plug-in finds a BSD disk label, it exports the BSD partitions. Because
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this primary partition is actually just a container that holds the BSD
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partitions, and not a data partition itself, it is not exported by the
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DOS plug-in.
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Embedded partitions are named after the primary partition they were
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discovered within. As an example, <TT
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CLASS="filename"
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>hda3.1</TT
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> is
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the name of the first embedded partition found within primary partition
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<TT
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CLASS="filename"
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>hda3</TT
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>.
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</P
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></DIV
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><DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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SUMMARY="Footer navigation table"
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="appxdos.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="34%"
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VALIGN="top"
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HREF="index.html"
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>Home</A
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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HREF="assigndos.html"
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ACCESSKEY="N"
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>Next</A
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></TR
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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>The DOS plug-in</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="appxdos.html"
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ACCESSKEY="U"
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>Up</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Assigning the DOS plug-in</TD
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></TR
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></TABLE
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></DIV
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></HTML
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> |