934 lines
19 KiB
HTML
934 lines
19 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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>Glossary (DRAFT, but not for long hopefully)</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="PREVIOUS"
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TITLE="ADDENDUM: How to use this License for
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your documents"
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HREF="gfdl-addendum.html"><LINK
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REL="NEXT"
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TITLE="Index-Draft"
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HREF="bookindex.html"></HEAD
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><BODY
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CLASS="GLOSSARY"
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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="gfdl-addendum.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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></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="bookindex.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="GLOSSARY"
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><H1
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><A
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NAME="GLOSSARY"
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></A
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>Glossary (DRAFT, but not for long hopefully)</H1
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><A
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NAME="AEN4895"
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></A
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><BLOCKQUOTE
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CLASS="BLOCKQUOTE"
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><P
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><SPAN
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CLASS="QUOTE"
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>"The Librarian of the Unseen University
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had unilaterally decided to aid comprehension
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by producing an Orang-utan/Human Dictionary.
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He'd been working on it for three months.
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It wasn't easy. He'd got as far as `Oook.'"</SPAN
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>
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(Terry Pratchett, ``Men At Arms'')</P
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></BLOCKQUOTE
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><P
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> This is a short list of word definitions for concepts
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relating to Linux and system administration. </P
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><DL
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><DT
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><B
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>CMOS RAM</B
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></DT
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><DD
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><P
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> CMOS stands for "Complementary Metal Oxide Semiconductor".
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It is a complex technology, but put very simply it is a type
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of transistor which maintains its state even if computer is
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powered off. This is due to a small battery on the motherboard.
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As a result, it does not lose what was stored on it when the
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power is switched off.
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</P
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></DD
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><DT
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><B
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>account</B
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></DT
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><DD
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><P
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> A Unix system gives users <I
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CLASS="GLOSSTERM"
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>accounts</I
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>. It
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gives them a username and a password with which to log on to the
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account. A home directory in which to store files is usually
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provided, and permissions to access hardware and software. These
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things taken as a whole are an <I
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CLASS="GLOSSTERM"
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>account</I
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>.
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</P
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></DD
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><DT
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><B
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>application program</B
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></DT
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><DD
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><P
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> Software that does something useful. The results of using an
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application program is what the computer was bought for.
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See also system program, operating system.
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</P
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></DD
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><DT
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><B
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>bad block</B
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></DT
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><DD
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><P
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> A block (usually one sector on a disk) that cannot reliably hold
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data.
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</P
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></DD
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><DT
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><B
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>bad sector</B
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></DT
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><DD
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><P
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> Similar to <I
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CLASS="GLOSSTERM"
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>bad block</I
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> but more precise in
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the case where a block and a sector may be of differing sizes.
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</P
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></DD
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><DT
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><B
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>boot sector</B
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></DT
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><DD
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><P
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> Usually the first sector on any given partition. It contains
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a very short program (on the order of a few hundred bytes) which
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will load and start running the operating system proper.
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</P
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></DD
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><DT
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><B
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>booting</B
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></DT
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><DD
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><P
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> Everything that happens between the time the computer is
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switched on and it is ready to accept commands/input from
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the user is known as <I
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CLASS="GLOSSTERM"
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>booting</I
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>.
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</P
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></DD
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><DT
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><B
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>bootstrap loader</B
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></DT
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><DD
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><P
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> A very small program (usually residing in ROM) which reads
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a fixed location on a disk (eg. the <I
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CLASS="GLOSSTERM"
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>MBR</I
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>)
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and passes control over to it. The data residing on that fixed
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location is, in general, slightly bigger and more sophisticated,
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and it then takes responsibility for loading the actual operating
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system and passing control to it.
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</P
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></DD
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><DT
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><B
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>cylinder</B
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></DT
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><DD
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><P
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> The set of <I
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CLASS="GLOSSTERM"
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>tracks</I
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> on a multi-headed disk
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that may be accessed without head movement. In other words the
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tracks which are the same distance from the spindle about which
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the disk <I
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CLASS="GLOSSTERM"
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>platters</I
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> rotate. Placing data
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that is more likely to be accessed at the same time on the same
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cylinder can reduce the access time significantly as moving the
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read-write heads is slow compared to the speed with which the
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disks rotate.
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</P
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></DD
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><DT
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><B
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>daemon</B
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></DT
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><DD
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><P
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> A process lurking in the background, usually unnoticed, until
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something triggers it into action. For example, the
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<B
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CLASS="COMMAND"
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>update</B
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>
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daemon wakes up every thirty seconds or so to flush the buffer
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cache, and the <B
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CLASS="COMMAND"
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>sendmail</B
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> daemon awakes whenever
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someone sends mail.
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</P
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></DD
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><DT
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><B
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>daylight savings time</B
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></DT
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><DD
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><P
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> A time of the year during which clocks are set forward one hour.
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Widely used around the world in summer so that evenings have more
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daylight than they would otherwise.
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</P
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></DD
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><DT
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><B
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>disk controller</B
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></DT
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><DD
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><P
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> A hardware circuit which translates instructions about disk access
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from the operating system to the physical disk. This provides a
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layer of abstraction that means that an operating system does not
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need to know how to talk to the many different types of disks, but
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only needs to know about the (comparatively low) number of types of
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disk controller. Common disk controller types are IDE and SCSI.
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</P
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></DD
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><DT
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><B
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>emergency boot floppy</B
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></DT
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><DD
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><P
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> A floppy disk which can be used to boot the system even
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if the hard disk has suffered damage on its filesystem.
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Most linux distributions offer to make one of these during
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installation, this is highly recommended. If your Linux
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distribution does not offer this facility then read the
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Boot floppy HOWTO, available at the LDP (**Find URL to cite**).
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</P
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></DD
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><DT
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><B
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>fibre channel</B
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></DT
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><DD
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><P
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> A high speed networking protocol primarily used in Storage
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Area Networks. Unlike it's name suggests, fibre channel can be
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ran over fiber optic, or copper cables.
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</P
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></DD
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><DT
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><B
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>filesystem</B
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></DT
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><DD
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><P
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> A term which is used for two purposes and which can have two
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subtly different meanings. It is either the collection of
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files and directories on a drive (whether hard drive, floppy,
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Cd-ROM, etc). Or it is the markers put onto the disk media
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which the OS uses to decide where to write files to (inodes,
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blocks, superblocks etc). The actual meaning can almost
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always be inferred from context.
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</P
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></DD
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><DT
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><B
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>formatting</B
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></DT
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><DD
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><P
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> Strictly, formatting is organizing and marking the surface of
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a disk into <I
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CLASS="GLOSSTERM"
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>tracks</I
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>, <I
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CLASS="GLOSSTERM"
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>sectors
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</I
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>, and <I
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CLASS="GLOSSTERM"
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>cylinders</I
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>. It is also
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sometimes (incorrectly) a term used to signify the action of
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writing a <I
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CLASS="GLOSSTERM"
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>filesystem</I
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> to a disk (especially
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in the MS Windows/MS DOS world).
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</P
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></DD
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><DT
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><B
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>fragmented</B
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></DT
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><DD
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><P
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> When a file is not written to a disk in contiguous <I
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CLASS="GLOSSTERM"
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> blocks</I
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>. If there is not enough free space to write
|
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a full file to a disk in one continuous stream of <I
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CLASS="GLOSSTERM"
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> blocks</I
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> then the file gets split up between two or
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more parts of the disk surface. This is known as <I
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|
CLASS="GLOSSTERM"
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|
> fragmenting</I
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> and can make the time for loading a
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file longer as the disk has to seek for the rest of the file.
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</P
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></DD
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><DT
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><B
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|
>full backup</B
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></DT
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><DD
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><P
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> Taking a copy of the whole filesystem to a backup media
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(eg tape, floppy, or CD).
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</P
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></DD
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><DT
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><B
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>geometry</B
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></DT
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><DD
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><P
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> How many cylinders, sectors per cylinder and heads a disk
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drive has.
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</P
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></DD
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><DT
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|
><B
|
|
>high level formatting</B
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|
></DT
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><DD
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><P
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|
> An incorrect term for writing a filesystem to a disk. Often
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used in the MS Windows and MS DOS world.
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</P
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></DD
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|
><DT
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|
><B
|
|
>incremental backups</B
|
|
></DT
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><DD
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><P
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|
> A backup of what has changed in a filesystem since the last
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<I
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|
CLASS="GLOSSTERM"
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>full backup</I
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>. <I
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CLASS="GLOSSTERM"
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|
>Incremental
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backups</I
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> if used sensibly as part of a backup regime,
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can save a lot of time and effort in maintaining a backup of data.
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</P
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></DD
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><DT
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><B
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>inode</B
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></DT
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><DD
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><P
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> A data structure holding information about files in a Unix
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file system. There is an inode for each file and a file is
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uniquely identified by the file system on which it resides
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and its inode number on that system. Each inode contains
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the following information: the device where the inode resides,
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|
locking information, mode and type of file, the number of links
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|
to the file, the owner's user and group ids, the number of bytes
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in the file, access and modification times, the time the inode
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itself was last modified and the addresses of the file's
|
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blocks on disk. A Unix directory is an association between
|
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file leafnames and inode numbers. A file's inode number
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can be found using the "-i" switch to ls.
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</P
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></DD
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><DT
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><B
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|
>iSCSI</B
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></DT
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><DD
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|
><P
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|
> A network storage protocol that enables the sending of SCSI commands
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over a TCP/IP network. Primarily used in Storage Area Networks.
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|
</P
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></DD
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|
><DT
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|
><B
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|
>kernel</B
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|
></DT
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|
><DD
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><P
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|
> Part of an operating system that implements the interaction with
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hardware and the sharing of resources. See also system program.
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</P
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></DD
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><DT
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><B
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>local time</B
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></DT
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><DD
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|
><P
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> The official time in a local region (adjusted for location around
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the Earth); established by law or custom.
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</P
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></DD
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><DT
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><B
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|
>logical partition</B
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></DT
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><DD
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|
><P
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> A partition inside an <I
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CLASS="GLOSSTERM"
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>extended partition</I
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>,
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which is ``logical'' in that it does not exist in reality,
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but only inside the logical structure of the software.
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</P
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></DD
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><DT
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|
><B
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|
>logical volume manager (LVM)</B
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></DT
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|
><DD
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><P
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|
> A collection of programs that allow larger physical
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disks to be reassembled into "logical" disks that can be shrunk or
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expanded as data needs change.
|
|
</P
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|
></DD
|
|
><DT
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|
><B
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|
>low level formatting</B
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|
></DT
|
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><DD
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><P
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|
> Synonymous with <I
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|
CLASS="GLOSSTERM"
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|
>formatting</I
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> and used in
|
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the MS DOS world so differentiate from creating a filesystem
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which is also known as formatting sometimes.
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</P
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|
></DD
|
|
><DT
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|
><B
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|
>mail transfer agent</B
|
|
></DT
|
|
><DD
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|
><P
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|
> (MTA) The program responsible for delivering e-mail messages.
|
|
Upon receiving a message from a <I
|
|
CLASS="GLOSSTERM"
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|
>mail user agent
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|
</I
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|
> or another MTA it stores it temporarily locally
|
|
and analyzes the recipients and either delivers it (local
|
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addressee) or forwards it to another MTA. In either case
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|
it may edit and/or add to the message headers. A widely used
|
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MTA for Unix is sendmail.
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</P
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|
></DD
|
|
><DT
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|
><B
|
|
>mail user agent</B
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|
></DT
|
|
><DD
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|
><P
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|
> (MUA) The program that allows the user to compose and read
|
|
electronic mail messages. The MUA provides the interface
|
|
between the user and the <I
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|
CLASS="GLOSSTERM"
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|
>mail transfer agent
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|
</I
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|
>. Outgoing mail is eventually handed over to an
|
|
MTA for delivery while the incoming messages are picked up
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from where the MTA left it (although MUAs running on
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single-user machines may pick up mail using POP).
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|
Examples of MUAs are pine, elm and mutt.
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</P
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|
></DD
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><DT
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|
><B
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|
>master boot record</B
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></DT
|
|
><DD
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|
><P
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|
> (MBR) The first logical sector on a disk, this is (usually)
|
|
where the BIOS looks to load a small program that will boot
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the computer.
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|
</P
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|
></DD
|
|
><DT
|
|
><B
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|
>network file system</B
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|
></DT
|
|
><DD
|
|
><P
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|
> (NFS) A protocol developed by Sun Microsystems, and defined in
|
|
RFC 1094 (FIND URL), which allows a computer to access files
|
|
over a network as if they were on its local disks.
|
|
</P
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|
></DD
|
|
><DT
|
|
><B
|
|
>operating system</B
|
|
></DT
|
|
><DD
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|
><P
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|
> Software that shares a computer system's resources (processor,
|
|
memory, disk space, network bandwidth, and so on) between
|
|
users and the application programs they run. Controls access
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|
to the system to provide security. See also kernel, system program,
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|
application program.
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|
</P
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|
></DD
|
|
><DT
|
|
><B
|
|
>partition</B
|
|
></DT
|
|
><DD
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|
><P
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|
> A logical section of a disk. Each partition normally has its
|
|
own file system. Unix tends to treat partitions as though
|
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they were separate physical entities.
|
|
</P
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|
></DD
|
|
><DT
|
|
><B
|
|
>password file</B
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|
></DT
|
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><DD
|
|
><P
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|
> A file that holds usernames and information about their accounts
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|
like their password. On Unix systems this file is usually
|
|
<TT
|
|
CLASS="FILENAME"
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|
>/etc/passwd</TT
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|
>. On most modern Linux systems
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|
the <TT
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|
CLASS="FILENAME"
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|
>/etc/passwd</TT
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|
> file does not actually hold
|
|
password data. That tends to be held in a different file <TT
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|
CLASS="FILENAME"
|
|
> /etc/shadow</TT
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|
> for security reasons. See manual pages
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|
passwd(5) and shadow(5) for more information.
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|
</P
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|
></DD
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><DT
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|
><B
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|
>physical extents</B
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|
></DT
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><DD
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><P
|
|
> A term used to describe a the chunks a physical volume is broken
|
|
down into when using the Logical Volume Manager.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>physical volume</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> A term used an actual disk partition, usually in reference to the
|
|
logical volume manager.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>platters</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> A physical disk inside a hard drive. Usually a hard drive is
|
|
made up of multiple physical disks stacked up on top of each
|
|
other. One individual disk is known as a <I
|
|
CLASS="GLOSSTERM"
|
|
>platter
|
|
</I
|
|
>.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>power on self test</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> (POST) A series of diagnostic tests which are run when a computer
|
|
is powered on. Typically this might include testing the memory,
|
|
testing that the hardware configuration is the same as the last
|
|
saved configuration, checking that any floppy drives, or hard
|
|
drives which are known about by the BIOS are installed and working.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>print queue</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> A file (or set of files) which the print <I
|
|
CLASS="GLOSSTERM"
|
|
>daemon
|
|
</I
|
|
><I
|
|
CLASS="GLOSSTERM"
|
|
> uses so that applications which wish to use the
|
|
printer do not have to wait until the print job they have sent
|
|
is finished before they can continue. It also allows multiple
|
|
users to share a printer.
|
|
</I
|
|
></P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>read-write head</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> A tiny electromagnetic coil and metal pole used to write and read
|
|
magnetic patterns on a disk. These coils move laterally against
|
|
the rotary motion on the <I
|
|
CLASS="GLOSSTERM"
|
|
>platters</I
|
|
>.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>root filesystem</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> The parent of all the other filesystems mounted in a Unix filesystem
|
|
tree. Mounted as / it might have other filesystems mounted on it
|
|
(/usr for example). If the root filesystem cannot be mounted then the
|
|
<I
|
|
CLASS="GLOSSTERM"
|
|
>kernel</I
|
|
> will panic and the system will not be
|
|
able to continue <I
|
|
CLASS="GLOSSTERM"
|
|
>booting</I
|
|
>
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>run level</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> Linux has up to 10 runlevels (0-9) available (of which usually only
|
|
the first 7 are defined). Each runlevel may start a different set
|
|
of services, giving multiple different configurations in the same
|
|
system. Runlevel 0 is defined as ``system halt'', runlevel 1 is
|
|
defined as ``<I
|
|
CLASS="GLOSSTERM"
|
|
>single user mode</I
|
|
>'', and runlevel
|
|
6 is defined as ``reboot system''. The remaining runlevels can,
|
|
theoretically, be defined by the system administrator in any way.
|
|
However most distributions provide some other predefined runlevels.
|
|
For example, runlevel 2 might be defined as ``multi-user console'',
|
|
and runlevel 5 as ``multi-user X-Window system''. These definitions
|
|
vary considerably from distribution to distribution, so please check
|
|
the documentation for your own distribution.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>sectors</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> The minimum <I
|
|
CLASS="GLOSSTERM"
|
|
>track</I
|
|
> length that can be
|
|
allocated
|
|
to store data. This is usually (but not always) 512 bytes.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>shadow passwords</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> Because the <I
|
|
CLASS="GLOSSTERM"
|
|
>password file</I
|
|
> on Unix systems
|
|
often
|
|
needs to be world readable it usually does not actually contain the
|
|
encrypted passwords for users' accounts. Instead a shadow file is
|
|
employed (which is not world readable) which holds the encrypted
|
|
passwords for users' accounts.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>single user mode</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> Usually runlevel 1. A runlevel where logins are not allowed except
|
|
by the root account. Used either for system repairs (if the
|
|
filesystem is partially damaged it may still be possible to boot into
|
|
runlevel 1 and repair it), or for moving filesystems around between
|
|
partitions. These are just two examples. Any task that requires a
|
|
system where only one person can write to a disk at a time is a
|
|
candidate for requiring runlevel 1.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>spool</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> To send a file (or other data) to a queue. Generally used in
|
|
conjunction with printers, but might also be used for other
|
|
things (mail for example). The term is reported to be an acronym
|
|
for ``Simultaneous Peripheral Operation On-Line'', but according
|
|
to the <A
|
|
HREF="http://www.tuxedo.org/~esr/jargon"
|
|
TARGET="_top"
|
|
>Jargon File
|
|
</A
|
|
> it may have been a backronym (something made up later
|
|
for effect).
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>system call</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> The services provided by the kernel to application programs,
|
|
and the way in which they are invoked. See section 2 of the
|
|
manual pages.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>swap space</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> Space on a disk in which the system can write portions of memory
|
|
to. Usually this is a dedicated partition, but it may also be
|
|
a swapfile.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>system program</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> Programs that implement high level functionality of an operating
|
|
system, i.e., things that aren't directly dependent on the
|
|
hardware. May sometimes require special privileges to run
|
|
(e.g., for delivering electronic mail), but often just commonly
|
|
thought of as part of the system (e.g., a compiler). See also
|
|
application program, kernel, operating system.
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>time drift</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> This is a term for a computers inaccuracy at keeping track of time.
|
|
All computers have some rate of error when keeping time. With newer
|
|
computers this rate of error is extremely small.</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>track</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> The part of a disk <I
|
|
CLASS="GLOSSTERM"
|
|
>platter</I
|
|
> which passes
|
|
under one <I
|
|
CLASS="GLOSSTERM"
|
|
>read-write head</I
|
|
> while the head
|
|
is stationary but the disk is spinning. Each track is divided
|
|
into <I
|
|
CLASS="GLOSSTERM"
|
|
>sectors</I
|
|
>, and a vertical collection of
|
|
tracks is a <I
|
|
CLASS="GLOSSTERM"
|
|
>cylinder</I
|
|
>
|
|
</P
|
|
></DD
|
|
><DT
|
|
><B
|
|
>volume group</B
|
|
></DT
|
|
><DD
|
|
><P
|
|
> A collection of physical volumes broken down into physical
|
|
extents, and available for use in logical partitions.
|
|
</P
|
|
></DD
|
|
></DL
|
|
></DIV
|
|
><DIV
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CLASS="NAVFOOTER"
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WIDTH="33%"
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VALIGN="top"
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><A
|
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HREF="gfdl-addendum.html"
|
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ACCESSKEY="P"
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>Prev</A
|
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>ADDENDUM: How to use this License for
|
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your documents</TD
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