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 physically¹ connected by cable within a limited geographical² area-typically in an office building or on a college campus. The topology of the network may be ring, star or bus. LANs use fiber³ 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.

网络有两类：局域网（LANs）和广域网（WAN）。在这里主要谈一下局域网。

局域网就是在一个有限的地域范围内，典型的如在办公大楼或校园中，将计算机及相关外设（如打印机）用电缆进行物理连结而组成的一个系统。网络的拓扑结构可以是环形的、星形的或总线形的。在局域网中，可用光纤或同轴电缆连结多台计算机，且每台计算机的硬盘上必须装有专门的通信软件。允许具有不同平台的计算机共存于同一局域网中，且能进行数据交换的软件早已开发出来了。