|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.
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.
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.
Novell公司的Net ware操作系统已经成为IBM公司特有的网络操作环境最强有力的竞争对手，它在对局域网络的支持方面也早于IBM公司。事实上，除了自己的一部分软件外，IBM公司也为所有的PC网和令牌环网购买了Net ware操作系统。Net ware 操作系统的最主要部分是文件服务器软件，服务器上的目录被映射到网络驱动器，这样在用户看来，它运行起来就如同是虚拟磁盘。它的服务器软件是一个多任务的操作系统，文件结构也与
DOS 2.x和DOS 3.x的文件结构一致。工作站上的 Net ware外壳程序拦截了DOS的21H中断，并重新走向为对服务器的调用。
Net ware操作系统的主要优点是能够运行在多种网络硬件上。不论是选择IBM网络，Corvus公司的OMNINET网络，还是AT＆T公司的星形局域网络等，都可获得Net ware的操作环境。