英语科普文选：Local Area Network(局域网)
<p> <span word="There">There</span> <span word="are">are</span> <span word="two">two</span> <span word="categories">categories</span> <span word="of">of</span> <span word="networks">networks</span>: <span word="local">local</span> <span word="area">area</span> <span word="networks">networks</span> (<span word="LANs">LANs</span>) <span word="and">and</span> <span word="wide">wide</span> <span word="area">area</span> <span word="networks">networks</span> (<span word="WANs">WANs</span>). <span word="Here">Here</span> <span word="I">I</span>'<span word="d">d</span> <span word="like">like</span> <span word="to">to</span> <span word="mainly">mainly</span> <span word="talk">talk</span> <span word="about">about</span> <span word="LAN">LAN</span>.</p><p> <span word="A">A</span> <span word="LAN">LAN</span> <span word="is">is</span> <span word="a">a</span> <span word="system">system</span> <span word="of">of</span> <span word="computers">computers</span> <span word="and">and</span> <span word="associated">associated</span> <span word="peripherals">peripherals</span> <span word="such">such</span> <span word="as">as</span> <span word="Printers">Printers</span> <span word="that">that</span> <span word="are">are</span> <span word="physically">physically</span> <span word="connected">connected</span> <span word="by">by</span> <span word="cable">cable</span> <span word="within">within</span> <span word="a">a</span> <span word="limited">limited</span> <span word="geographical">geographical</span> <span word="area">area</span>-<span word="typically">typically</span> <span word="in">in</span> <span word="an">an</span> <span word="office">office</span> <span word="building">building</span> <span word="or">or</span> <span word="on">on</span> <span word="a">a</span> <span word="college">college</span> <span word="campus">campus</span>. <span word="The">The</span> <span word="topology">topology</span> <span word="of">of</span> <span word="the">the</span> <span word="network">network</span> <span word="may">may</span> <span word="be">be</span> <span word="ring">ring</span>, <span word="star">star</span> <span word="or">or</span> <span word="bus">bus</span>. <span word="LANs">LANs</span> <span word="use">use</span> <span word="fiber">fiber</span> <span word="optics">optics</span> <span word="or">or</span> <span word="coaxial">coaxial</span> <span word="cable">cable</span> <span word="to">to</span> <span word="connect">connect</span> <span word="computers">computers</span>, <span word="and">and</span> <span word="each">each</span> <span word="computer">computer</span> <span word="must">must</span> <span word="have">have</span> <span word="special">special</span> <span word="communications">communications</span> <span word="software">software</span> <span word="installed">installed</span> <span word="oil">oil</span> <span word="its">its</span> <span word="hard">hard</span> <span word="disk">disk</span>. <span word="Software">Software</span> <span word="has">has</span> <span word="been">been</span> <span word="developed">developed</span> <span word="that">that</span> <span word="allows">allows</span> <span word="computers">computers</span> <span word="with">with</span> <span word="different">different</span> <span word="platforms">platforms</span> <span word="to">to</span> <span word="coexist">coexist</span> <span word="and">and</span> <span word="exchange">exchange</span> <span word="data">data</span> <span word="on">on</span> <span word="the">the</span> <span word="same">same</span> <span word="LAN">LAN</span>.</p><p> <span word="A">A</span> <span word="File">File</span> <span word="Server">Server</span></p><p> <span word="Many">Many</span> <span word="networks">networks</span> <span word="are">are</span> <span word="managed">managed</span> <span word="by">by</span> <span word="a">a</span> <span word="computer">computer</span> <span word="called">called</span> <span word="a">a</span> <span word="file">file</span> <span word="server">server</span>.<span word="A">A</span> <span word="file">file</span> <span word="server">server</span> <span word="has">has</span> <span word="a">a</span> <span word="large">large</span>－<span word="capacity">capacity</span> <span word="hard">hard</span> <span word="disk">disk</span> <span word="and">and</span> <span word="special">special</span> <span word="software">software</span> <span word="that">that</span> <span word="manages">manages</span> <span word="access">access</span> <span word="to">to</span> <span word="flies">flies</span> <span word="on">on</span> <span word="the">the</span> <span word="network">network</span>. <span word="It">It</span> <span word="controls">controls</span> <span word="how">how</span> <span word="data">data</span> <span word="and">and</span> <span word="database">database</span> <span word="are">are</span> <span word="shared">shared</span> <span word="among">among</span> <span word="users">users</span> <span word="on">on</span> <span word="the">the</span> <span word="network">network</span> <span word="and">and</span> <span word="how">how</span> <span word="users">users</span> <span word="access">access</span> <span word="master">master</span> <span word="copies">copies</span> <span word="of">of</span> <span word="data">data</span> <span word="and">and</span> <span word="application">application</span> <span word="software">software</span> <span word="on">on</span> <span word="the">the</span> <span word="centralized">centralized</span> <span word="hard">hard</span> <span word="disk">disk</span>. <span word="It">It</span> <span word="is">is</span> <span word="the">the</span> <span word="file">file</span> <span word="server">server</span>'<span word="s">s</span> <span word="job">job</span> <span word="to">to</span> <span word="make">make</span> <span word="sure">sure</span> <span word="that">that</span> <span word="users">users</span> <span word="don">don</span>'<span word="t">t</span> <span word="accidentally">accidentally</span> <span word="try">try</span> <span word="to">to</span> <span word="update">update</span> <span word="a">a</span> <span word="file">file</span> <span word="at">at</span> <span word="the">the</span> <span word="same">same</span> <span word="time">time</span> <span word="and">and</span> <span word="scramble">scramble</span> <span word="the">the</span> <span word="data">data</span>. <span word="The">The</span> <span word="file">file</span> <span word="server">server</span> <span word="may">may</span> <span word="also">also</span> <span word="manage">manage</span> <span word="the">the</span> <span word="access">access</span> <span word="to">to</span> <span word="an">an</span> <span word="expensive">expensive</span> <span word="piece">piece</span> <span word="of">of</span> <span word="hardware">hardware</span> <span word="such">such</span> <span word="as">as</span> <span word="a">a</span> <span word="laser">laser</span> <span word="printer">printer</span>.</p><p> <span word="When">When</span> <span word="a">a</span> <span word="file">file</span> <span word="server">server</span> <span word="is">is</span> <span word="used">used</span> <span word="on">on</span> <span word="a">a</span> <span word="LAN">LAN</span>, <span word="large">large</span> <span word="databases">databases</span> <span word="are">are</span> <span word="stored">stored</span> <span word="on">on</span> <span word="the">the</span> <span word="server">server</span> <span word="and">and</span> <span word="users">users</span> <span word="may">may</span> <span word="store">store</span> <span word="all">all</span> <span word="of">of</span> <span word="their">their</span> <span word="work">work</span> <span word="flies">flies</span> <span word="there">there</span> <span word="as">as</span> <span word="well">well</span>.<span word="This">This</span> <span word="operation">operation</span> <span word="is">is</span> <span word="analogous">analogous</span> <span word="to">to</span> <span word="someone">someone</span>'<span word="s">s</span> <span word="manually">manually</span> <span word="collecting">collecting</span> <span word="all">all</span> <span word="the">the</span> <span word="data">data</span> <span word="each">each</span> <span word="day">day</span> <span word="placing">placing</span> <span word="them">them</span> <span word="in">in</span> <span word="a">a</span> <span word="file">file</span> <span word="drawer">drawer</span>, <span word="and">and</span> <span word="then">then</span> <span word="redistributing">redistributing</span> <span word="these">these</span> <span word="data">data</span> <span word="to">to</span> <span word="the">the</span> <span word="workers">workers</span> <span word="as">as</span> <span word="needed">needed</span>.</p>
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