什么是局域網

　　局域網指有限區(qū)域(如辦公室或樓層)內的多臺計算機通過共享的傳輸介質互連，所組成的封閉網絡。接下來小編為大家整理了什么是局域網，希望對你有幫助哦!

　　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 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.

　　The LAN Operating System——Net Ware

　　Novell's Net ware has become the strongest competitor to IBM's 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 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 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 Novell's system of bridges and gateways.

　　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 server's job to make sure that users don't accidentally try to update 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 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.

　　局域網

　　網絡有兩類：局域網(LANs)和廣域網(WAN)。在這里主要談一下局域網。

　　局域網就是在一個有限的地域范圍內，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機共存于同一局域網中，且能進行數(shù)據(jù)交換的軟件早已開發(fā)出來了。

　　局域網絡操作系統(tǒng)——Net ware

　　Novell公司的Net ware操作系統(tǒng)已經成為IBM公司特有的網絡操作環(huán)境最強有力的競爭對手，它在對局域網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網和令牌環(huán)網購買了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絡驅動器，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。工作站上的 Net ware外殼程序攔截了DOS的21H中斷，并重新走向為對服務器的調用。

　　Net ware操作系統(tǒng)的主要優(yōu)點是能夠運行在多種網絡硬件上。不論是選擇IBM網絡，Corvus公司的OMNINET網絡，還是AT&T公司的星形局域網絡等，都可獲得Net ware的操作環(huán)境。

　　文件服務器

　　許多網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上文件訪問的專門軟件。它控制著網上用戶如何共享數(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。