英语科普文选：LocalAreaNetwork(局域网)

文章作者 100test 发表时间 2007:08:06 13:02:41
来源 100Test.Com百考试题网

Local Area Network

　　There are two categories of networks: local area networks (LANs) and wide area networks (WANs). Here Id like to mainly talk about LAN.

　　A LAN is a system of computers and associated peripherals such as Printers that are physically connected by cable within a limited geographical area-typically in an office building or on a college campus. The topology of the network may be ring, star or bus. LANs use fiber optics or coaxial cable to connect computers, and each computer must have special communications software installed oil its hard disk. Software has been developed that allows computers with different platforms to coexist and exchange data on the same LAN.

A File Server

　　Many networks are managed by a computer called a file server.A file server has a large－capacity hard disk and special software that manages access to flies on the network. It controls how data and database are shared among users on the network and how users access master copies of data and application software on the centralized hard disk. It is the file servers job to make sure that users dont accidentally try to 0update a file at the same time and scramble the data. The file server may also manage the access to an expensive piece of hardware such as a laser printer.

　　When a file server is used on a LAN, large databases are stored on the server and users may store all of their work flies there as well.This operation is analogous to someones manually collecting all the data each day placing them in a file drawer, and then redistributing these data to the workers as needed.

The LAN Operating System--Net Ware

　　Novells Net ware has become the strongest competitor to IBMs own network operating environment and predates IBM in its support for LANs. In fact,IBM now markets Net ware for both the PC Network and for Token Ring in addition to its own software.The key to Net ware is the file server software and directories on the server are mapped to network drives, thus operating like virtual diskettes from a users perspective. The server software is a multitasking operating system with a file structure consistent with DOS 2.x and DOS 3.x. The Net ware shell in each workstation intercepts 21H DOS calls and redirects appropriate calls to the server.

　　Perhaps the primary advantage of Net ware is that it runs on a wide variety of networking hardware.Regardless of whether you choose an IBM network, Corvus OMNINET, AT＆T Star LAN, etc., you can obtain Net ware as the operating environment. In fact, if you have one of each the user will not be able to tell the difference(unless there are some distinct performance differentials), and they can be interconnected through Novells system of bridges and gateways.