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
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
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
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
- 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
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
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.
Remote Access & Modem
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
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.