局域网有几种工作模式，其中，在(20)中，若干台微机工作站与一台或多台文件服务器通过通信线路连接起来组成工作站存取服务器文件，共享存储设备。

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User　programs　interact　with　the　kernel　through　a　set　of　standard(71).　They　request　services　to　be　provided　by　the　kernel.　Such　services　would　include　accessing　a　file:　open　close,　read,　write,　link,　or　execute　a　file;　starting　or(72)accounting　records;　changing　ownership　of　a　file　or(73);　changing　to　a　new　directory;　creating,(74),　or　killing　a　process;　enabling　access　to　hardware　devices;　and　setting　limits　on　system　resources.　Unix　is　a　multi　-user,　multi　-tasking　operating　system.　You　can　have　many　users　logged　into　a　system　simultaneously,　each　running　many　programs.　It's　the　kernel's　job　to　keep　each　process　and　user　separate　and　to　regulate　access　to(75),　including　cpu,　memory,　disk　and　other　L/O　devices.

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