英語詩歌英語科普文選：Local Area Network(局域網(wǎng))

1、英語詩歌英語科普文選：Local Area Network(局域網(wǎng))    英語科普文選：Local Area Network(局域網(wǎng))There are two categories of networks: local area networks (LANs) and wide area networks (WANs). Here I'd like to mainly talk about LAN.A LAN is a system of computers and associated peripherals such as Printer

2、s 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 so

3、ftware 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 ServerMany networks are managed by a computer called a file server.A file server has a largecapacity hard disk and special software that

4、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 server's job to make sure that users don't accidentally try to upda

5、te 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 operatio

6、n is analogous to someone's 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 WareNovell's Net ware has become the strongest competitor to IBM's own network operating environme

7、nt 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 f

8、rom a user's 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 t

9、hat it runs on a wide variety of networking hardware.Regardless of whether you choose an IBM network, Corvus OMNINET, ATT 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 dist

10、inct performance differentials), and they can be interconnected through Novell's system of bridges and gateways. 局域網(wǎng)網(wǎng)絡有兩類：局域網(wǎng)（LANs）和廣域網(wǎng)（WAN）。在這里主要談一下局域網(wǎng)。局域網(wǎng)就是在一個有限的地域范圍內(nèi)，典型的如在辦公大樓或校園中，將計算機及相關外設（如打印機）用電纜進行物理連結而組成的一個系統(tǒng)。網(wǎng)絡的拓撲結構可以是環(huán)形的、星形的或總線形的。在局域網(wǎng)中，可用光纖或同軸電纜連結多臺計算機，且每臺計算機的硬盤上必須裝有專門的通信軟件。允許具有不同平臺的計算

11、機共存于同一局域網(wǎng)中，且能進行數(shù)據(jù)交換的軟件早已開發(fā)出來了。文件服務器許多網(wǎng)絡由一稱為文件服務器的計算機來管理。文件服務器具有大容量的硬盤和一些用來管理對網(wǎng)上文件訪問的專門軟件。它控制著網(wǎng)上用戶如何共享數(shù)據(jù)和數(shù)據(jù)庫，以及用戶如何存取中央硬盤上的數(shù)據(jù)和應用軟件的主拷備。確保兩個用戶不能偶然地在同一時刻對同一文件進行更新或爭奪數(shù)據(jù)也是文件服務器的工作。文件服務器還可以管理對昂貴硬件（如激光打印機）的訪問。當文件服務器用于局域網(wǎng)時，大型數(shù)據(jù)庫就被存儲在服務器上，而且用戶也可以將其所有的工作文件存放在上面。這就像是一個人每天手工收集所有的數(shù)據(jù)，放到一文件抽屜中，然后等需要時，再將這些數(shù)據(jù)發(fā)到工作人員手中。局域網(wǎng)絡操作系統(tǒng)Net wareNovell公司的Net ware操作系統(tǒng)已經(jīng)成為IBM公司特有的網(wǎng)絡操作環(huán)境最強有力的競爭對手，它在對局域網(wǎng)絡的支持方面也早于IBM公司。事實上，除了自己的一部分軟件外，IBM公司也為所有的PC網(wǎng)和令牌環(huán)網(wǎng)購買了Net ware操作系統(tǒng)。Net ware 操作系統(tǒng)的最主要部分是文件服務器軟件，服務器上的目錄被映射到網(wǎng)絡驅(qū)動器，這樣在用戶看來，它運行起來就如同是虛擬磁盤。它的服務器軟件是一個多任務的操作系統(tǒng)，文件結構也與DOS 2.x和DOS 3.x的文件結構一致。工