217 lines
5.0 KiB
HTML
217 lines
5.0 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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>CD-ROMs</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="Linux System Administrators Guide"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Using Disks and Other Storage Media"
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HREF="disk-usage.html"><LINK
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REL="PREVIOUS"
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TITLE="Floppies"
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HREF="floppies.html"><LINK
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REL="NEXT"
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TITLE="Tapes"
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HREF="tapes.html"></HEAD
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><BODY
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CLASS="SECT1"
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#840084"
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ALINK="#0000FF"
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><DIV
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CLASS="NAVHEADER"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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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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>Linux System Administrators 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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><A
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HREF="floppies.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="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 5. Using Disks and Other Storage Media</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="tapes.html"
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ACCESSKEY="N"
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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="CDROM"
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></A
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>5.6. CD-ROMs</H1
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><P
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>A CD-ROM drive uses an
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optically read, plastic coated disk.
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The information is recorded on the surface of the disk
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in small `holes' aligned along a spiral from the center to the edge.
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The drive directs a laser beam along the spiral to read the disk.
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When the laser hits a hole, the laser is reflected in one way; when
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it hits smooth surface, it is reflected in another way. This makes
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it easy to code bits, and therefore information. The rest is easy,
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mere mechanics.</P
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><P
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>CD-ROM drives are slow compared to hard disks. Whereas a
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typical hard disk will have an average seek time less than 15
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milliseconds, a fast CD-ROM drive can use tenths of a second for
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seeks. The actual data transfer rate is fairly high at hundreds of
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kilobytes per second. The slowness means that CD-ROM drives are not
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as pleasant to use as hard disks (some Linux distributions provide
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`live' filesystems on CD-ROMs, making it unnecessary to copy the
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files to the hard disk, making installation easier and saving a lot
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of hard disk space), although it is still possible. For installing
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new software, CD-ROMs are very good, since maximum speed is not
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essential during installation.</P
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><P
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>There are several ways to arrange data on a CD-ROM. The most
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popular one is specified by the international standard ISO 9660
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.
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This standard specifies a very minimal filesystem, which is even
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more crude than the one MS-DOS uses. On the other hand, it is so
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minimal that every operating system should be able to map it to its
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native system.</P
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><P
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>For normal UNIX use, the ISO 9660 filesystem is not usable, so
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an extension to the standard has been developed, called the Rock
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Ridge extension. Rock Ridge
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allows longer filenames, symbolic
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links, and a lot of other goodies, making a CD-ROM look more or less
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like any contemporary UNIX filesystem. Even better, a Rock Ridge
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filesystem is still a valid ISO 9660 filesystem, making it usable by
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non-UNIX systems as well. Linux supports both ISO 9660 and the Rock
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Ridge extensions; the extensions are recognized and used
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automatically.</P
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><P
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>The filesystem is only half the battle, however. Most CD-ROMs
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contain data that requires a special program to access, and most of
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these programs do not run under Linux (except, possibly, under
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dosemu, the Linux MS-DOS emulator, or wine, the Windows emulator.
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</P
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><P
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>Ironically perhaps, wine actually stands for ``Wine Is Not an
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Emulator''.
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Wine, more strictly, is an API (Application Program
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Interface) replacement. Please see the wine documentation at
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<A
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HREF="http://www.winehq.com"
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TARGET="_top"
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>http://www.winehq.com</A
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>
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for more information.</P
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><P
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>There is also VMWare, a commercial product, which emulates
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an entire x86 machine in software. See the VMWare website,
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<A
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HREF="http://www.vmware.com"
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TARGET="_top"
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>http://www.vmware.com</A
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>
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for more information.</P
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><P
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>A CD-ROM drive is accessed via the corresponding device file.
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There are several ways to connect a CD-ROM drive to the computer:
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via SCSI, via a sound card, or via EIDE. The hardware hacking
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needed to do this is outside the scope of this book, but the
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type of connection decides the device file.</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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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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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="floppies.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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ALIGN="center"
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VALIGN="top"
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><A
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HREF="index.html"
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ACCESSKEY="H"
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>Home</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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><A
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HREF="tapes.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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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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>Floppies</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="disk-usage.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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>Tapes</TD
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></TR
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></TABLE
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></DIV
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></BODY
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></HTML
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> |