A network is a group of two or more computers that intelligently share hardware or software devices with each other. A network can be as small and simple as two computers that share the printer and CD-ROM drive attached to one of them or as large as the world's largest network: the Internet.

Intelligently sharing means that each computer that shares resources with another computer or computers maintains control of that resource. Thus, a switchbox for sharing a single printer between two computers doesn't qualify as a network device; because the switchbox—not the computers—handles the print jobs, neither computer knows when the other one needs to print, and print jobs can interfere with each other.

A shared printer, on the other hand, can be controlled remotely and can store print jobs from different computers on the print server's hard disk. Users can change the sequence of print jobs, hold them, or cancel them. And, sharing of the device can be controlled through passwords, further differentiating it from a switchbox.

Virtually any storage or output device can be shared over a network, but the most common devices include:

• Printers

• Disk drives

• CD-ROM and optical drives

• Modems

• Fax machines

• Tape backup units

• Scanners

Entire drives, selected folders, or individual files can be shared with other users via the network.

In addition to reducing hardware costs by sharing expensive printers and other peripherals among multiple users, networks provide additional benefits to users:

• Multiple users can share access to software and data files.

• Electronic mail (email) can be sent and received.

• Multiple users can contribute to a single document using collaboration features.

• Remote-control programs can be used to troubleshoot problems or show new users how to perform a task.

• A single Internet connection can be shared among multiple computers.

Types of Networks

Several types of networks exist, from small, two-station arrangements to networks that interconnect offices in many cities:

• Local area networks. The smallest office network is referred to as a local area network (LAN). A LAN is formed from computers and components in a single office or building. A LAN can also be built at home from the same components used in office networking, but, as you'll see later, special home-networking components now exist to allow the creation of what can be called a home area network (HAN).

• Home area networks. A home area network (HAN) often uses the same hardware components as a LAN, but it is mainly used to share Internet access. Powerline, low-speed wireless, and phoneline networks are used primarily in HAN rather than LAN environments. HANs are often referred to as small-office/home-office (SOHO) LANs.

• Wide area networks. LANs in different locations can be connected together by high-speed fiber-optic, satellite, or leased phone lines to form a wide area network (WAN).

• The Internet. The World Wide Web is the most visible part of the world's largest network, the Internet. Although many users of the Internet still use modems over a dialup connection rather than a LAN or WAN connection, any user of the Internet is a network user.

The Internet is really a network of networks, all of which are connected to each other through the TCP/IP protocol. Programs such as Web browsers, File Transfer Protocol (FTP) clients, and newsreaders are some of the most common ways users work with the Internet.

• Intranets. Intranets use the same Web browsers and other software and the same TCP/IP protocol as the public Internet, but intranets exist as a portion of a company's private network. Typically, intranets comprise one or more LANs that are connected to other company networks, but, unlike the Internet, the content is restricted to authorized company users only. Essentially, an intranet is a private Internet.

• Extranets. Intranets that share a portion of their content with customers, suppliers, or other businesses, but not with the general public, are called extranets. As with intranets, the same Web browsers and other software are used to access the content.

Requirements for a Network

Unless the computers that are connected know they are connected and agree on a common means of communication and what resources are to be shared, they can't work together. Networking software is just as important as networking hardware because it establishes the logical connections that make the physical connections work.

At a minimum, each network requires the following:

• Physical (cable) or wireless (infrared [IRDA] or radio-frequency) connections between computers

• A common set of communications rules, known as a network protocol

• Software that enables resources to be shared with other PCs and controls access to shared resources, known as a network operating system

• Resources that can be shared, such as printers, disk drives, and CD-ROMs

• Software that enables computers to access other computers with shared resources, known as a network client

These rules apply to the simplest and most powerful networks, and all the ones in between, regardless of their nature.