Network require special software to control the flow of information between users. A Network Operating System, or NOS, is installed onto each PC that requires network access. The NOS is like a traffic cop that monitors the exchange and flow of files, electronic mail, and other network information. 

Network Operating Systems are classified according to whether they are peer-to-peer or client-server NOSs.  Peer-to-peer NOSs like Windows 95, Windows98 and Windows for Workgroups are best for home & small office use...   they are great for sharing applications, data, printers, and other localized resources across a few PCs. Client-server NOSs like Windows NT, Linux and NetWare are ideal for large-scale organizations that require fast network access for video, publishing, multimedia, spreadsheet, database, and accounting operations. 

A peer-to-peer network allows two or more PCs to pool their resources together. Individual resources like disk drives, CD-ROM drives, and even printers are transformed into shared, collective resources that are accessible from every PC. 

Unlike client-server networks, where network information is stored on a centralized file server PC and made available to tens, hundreds, or thousands client PCs, the information stored across peer-to-peer networks is uniquely decentralized. Because peer-to-peer PCs have their own hard disk drives that are accessible by all computers, each PC acts as both a client (information requestor) and a server (information provider). In the diagram below, three peer-to-peer workstations are shown. Although not capable of handling the same amount of information flow that a client-server network might, all three computers can communicate directly with each other and share one another's resources.

A peer-to-peer network can be built with either 10BaseT cabling and a hub or with a thin coax backbone. 10BaseT is best for small workgroups of 16 or fewer users that do not span long distances, or for workgroups that have one or more portable computers that may be disconnected from the network from time to time. 

After the networking hardware has been installed, a peer-to-peer network software package must be installed onto all of the PCs. Such a package allows information to be transferred back and forth between the PCs, hard disks, and other devices when users request it. Popular peer-to-peer NOS software includes Windows98, Windows 95, Windows for Workgroups, Artisoft LANtastic, and NetWare Lite. 

Most NOSs allow each peer-to-peer user to determine which resources will be available for use by other users.  Specific hard & floppy disk drives, directories or files, printers, and other resources can be attached or detached from the network via software. When one user's disk has been configured so that it is "sharable", it will usually appear as a new drive to the other users. In other words, if user A has an A and C drive on his computer, and user B configures his entire C drive as sharable, user A will suddenly have an A, C, and D drive (user A's D drive is actually user B's C drive). Directories work in a similar fashion. If user A has an A & C drive, and user B configures his "C:\WINDOWS" and "C:\DOS" directories as sharable, user A may suddenly have an A, C, D, and E drive (user A's D is user B's C:\WINDOWS, and E is user B's C:\DOS).  I hope you got all of that? 

Because drives can be easily shared between peer-to-peer PCs, applications only need to be installed on one computer...   not two or three. If users have one copy of Microsoft Word, for example, it can be installed on user A's computer...   and still used by user B. 

The advantages of peer-to-peer over client-server NOSs include:

• No need for a network administrator
• Network is fast/inexpensive to setup & maintain
• Each PC can make backup copies of its data to other PCs for security. 
• Easiest type of network to build, peer-to-peer is perfect for both home and office use.

 

In a client-server environment like Windows NT or Novell NetWare, files are stored on a centralized, high speed file server PC that is made available to client PCs. Network access speeds are usually faster than those found on peer-to-peer networks, which is reasonable given the vast numbers of clients that this architecture can support.  Nearly all network services like printing and electronic mail are routed through the file server, which allows networking tasks to be tracked. Inefficient network segments can be reworked to make them faster, and users' activities can be closely monitored.  Public data and applications are stored on the file server, where they are run from client PCs' locations, which makes upgrading software a simple task--network administrators can simply upgrade the applications stored on the file server, rather than having to physically upgrade each client PC.

In the client-server diagram above, the client PCs are shown to be separate and subordinate to the file server.  The clients' primary applications and files are stored in a common location. File servers are often set up so that each user on the network has access to his or her "own" directory, along with a range of  "public" directories where applications are stored.  If the two clients above want to communicate with each other, they must go through the file server to do it. A message from one client to another is first sent to the file server, where it is then routed to its destination.  With tens or hundreds of client PCs, a file server is the only way to manage the often complex and simultaneous operations that large networks require.

 

In client-server networks, network printing is normally handled by a print server, a small box with at least two connectors: one for a printer, and another that attaches directly to the network cabling. Some print servers have more than two ports...  they may, for example, support 2, 3, or 4 printers simultaneously. When a user sends a print job, it travels over the network cabling to the file server where it is stored. When the print server senses that the job is waiting, it moves it from the file server to its attached printer. When the job is finished, the print server returns a result message to the file server, indicating that the process is complete. 

In the diagram below, the client PC sends a job to the file server. The file server, in turn, forwards the job to the print server, which sends it to the printer when it's available. Any client on the network can access the printer in this fashion, and it's quite fast. The print server can be placed anywhere on the network, and a network can have more than one print server...  possibly one in an office's accounting department, another in marketing, and so on. 

Print Servers are available for both client-server and peer-to-peer networks. They're incredibly convenient because they let you put a printer anywhere along your network even if there isn't a computer nearby.  However, users often opt not to use a print-server with their peer-to-peer network. Why? Because every computer's resources are available to everyone on the network, A can print a job on B's printer...  just as if A had a printer attached to her computer. In this example, the printer is attached to the computer on the right. When the PC on the left sends a job, it "thinks" that it is printing to a printer of its own.  In actuality, the job travels over the network cables to the PC on the right, which stores and prints the job in the background. The user at the PC with the printer is never interrupted while his computer processes and prints the job transparently. 

 

When a client-server network needs a gateway to the world, the network administrator usually installs a remote-node server, which serves up two functions: remote access and modem sharing. Most remote-node servers attach directly to the network cabling; they provide a bridge between the network, a modem, and a telephone line.

Remote access allows users to dial into their home networks from anywhere in the world. Once a  connection has been established over ordinary phone lines by modem, users can access any programs or data on the network just as if they were seated at one of its local workstations.  Some remote access servers only provide access to a file server's disk drives. Others can provide access to both the file server and direct access to any PC's hard disk on the network. This saves time because it allows a remote user to communicate directly with any network user without having to go through the file server. 

Modem sharing lets local network users dial out from their individual network computers to access the Internet.  After firing up their favorite communications software, local users establish a link with the remote-node server over the network, which opens up an outgoing telephone line.  Users' individual PCs don't need modems, which is a big money saver...  only a single modem & phone line are required for tens or hundreds of users. In the case of peer-to-peer networks, by contrast, every PC requires its own modem for access to the outside world, unless you use special software packages like Wingate or Sygate that can provide the same ability to a Peer-to-Peer network.