The word network has several definitions. The most commonly used meaning
describes the methods people use to maintain relationships with friends and
business contacts. Applied to computers, the term has a similar definition. A
network is a way to connect computers together so that the' communicate,
exchange information, and pool resources. In business, networks have
revolutionized the use of computer technology. Many businesses that used to rely
on a centralized system with a mainframe and a collection of terminals
(input/output devices that are connect mainframes and do not have the same
features as PCs) now use eom networks in which every employee who needs a
computer has a per computer connected to the network. Computer technology and
expertise no longer centralized in a company's mainframe and information systems
departments. The technology and expertise are distributed throughout
organization among a network of computers and computer literate. In education,
schools have also shifted to strategies built around networks personal
computers. These include LANs (local area networks), and network that connects
the computers and printers in a computer to a WANs (wide area
networks)--especially the Internet.
Whatever the setting, networks provide tremendous benefits. Four most
compelling benefits are:
Allowing simultaneous access to critical programs and data
Allowing people to share peripheral devices, such as printers and scanners
Streamlining personal communication with e-mail
Making the backup process easier
The following sections examine each of these advantages in more detail.
Simultaneous Access
It is a fact of business computing that multiple employees, using a computer
network, often need access to the same data at the same time. Without a net-work
that enables file sharing, employees keep separate copies of data on different
hard disks, and universally updating the data becomes very difficult. As soon as
a change is made to the data on one machine, a discrepancy arises, and it
quickly becomes difficult to know which set of data is correct. Storing data
that is used by more than one person on a shared storage device makes it
possible to solve the problem.
It is also true that most office workers use the same programs. One solution
to purchasing separate copies of applications for every worker is to use network
versions of programs. These programs are designed so that only one copy of the
application needs to be stored on the network server (called an application
server), with a minimum number of supporting files copied to each employee's
computer. A network server is a large central computer. (If the server stores
data files for users to access, it is commonly called a file server.) When
employees need to use a program, they simply load it from a shared storage
device into the RAM of their own desktop computers, as shown in Figure 7.1.
A network version of a software application is also a more efficient use of
hard disk space because many users can access a single shared copy instead of
storing separate copies on each user's hard disk.
Some software designed for networks is classified as groupware. This type of
software includes scheduling software, e-mail, and document management software.
Groupware allows multiple users on a network to cooperate on projects. Users can
work on the same documents, share their insights, and keep each other abreast of
their schedules so that meetings can be set up easily. Lotus Notes and Microsoft
Exchange are perhaps the best known examples of groupware, although there are
many competitors.
Shared Peripheral Devices
Perhaps the best incentive for small businesses to link computers in a
network is to share peripheral devices, especially expensive ones such as laser
printers, large hard disks, and scanners, as shown in Figure 7.2.
Many high quality laser printers cost more than $2,000, so it is not very
cost-effective for each user to have one. Sharing a laser printer on a network
makes the cost much less prohibitive. By using a process called spooling,
multiple users can send multiple print jobs to a printer. (Spooling can also
occur when a computer is not connected to a network, and multiple print jobs
are sent to a non-networked printer.) When users print a document or other file
to a net-worked printer (known as a print job), each job is stored in a
temporary spool file on the file server. As the printer finishes printing a
current job, the file server sends the next spooled job to the printer so that
it can be printed. Typically, a banner page is printed at the beginning of a new
job to separate print jobs.
Personal Communication
One of the most far reaching applications of data communications is electronic
mail (e-mail), a system for exchanging written messages (and increasingly, voice
and video messages) through a network. E-mail is some-thing of a cross between
the postal system and a telephone answering system. In an e-mail system, each
user has a unique address. To send someone an e-mail message, you enter the
person's e-mail address and then type the message. When you are finished, the
message is sent to the e-mail address. The next time that user accesses the
e-mail system, it reports that mail has arrived. Some systems notify the
recipient as each message arrives by flashing a message on the computer screen
or beeping. After reading the message, the recipient can save it, delete it,
forward it to someone else, or respond by sending back a reply message. Figure
7.3 shows the process for sending and receiving e-mail.
In addition to sending a page or pages of mail text, many systems allow you
to attach data files--such as spreadsheet files or word processed documents--to
your message. This means that an e-mail system allows people to share files even
when they do not have access to the same storage devices. For example, a local
area network also may have a connection to a large information network, such as
America Online, Microsoft Network, or the Internet. In this case, the person on
the local network can share files with anyone on the large information network.
E-mail is both efficient and inexpensive. Users can send written messages
without worrying about whether the other user's computer is currently running.
On centralized networks, the message is delivered almost instantaneously, and
the cost of sending the message is negligible. E-mail has provided the modem
world with an entirely new and immensely valuable form of communication
In addition to e-mail, the spread of networking technology is adding to the
popularity of teleconferencing and videoconferencing. A teleconference is a
virtual meeting in which a group of people in different locations conducts
discussions by typing messages to each other. Each message can be seen by all
the other people in the teleconference. Teleconference software has become more
sophisticated, gradually adding such features as a shared scratch pad where
diagrams or pictures can be drawn or electronically pasted.
The spread of networking is adding to the popularity of collaborative
software, which allows users to connect with one another over LAN or modem links
so that they can see what's happening on other users' computers. It lets people
send messages, exchange files, and sometimes even work on the same document at
the same time. If users have the necessary hardware and software, they can
actually see and speak to each other as they meet online (instead of merely
typing messages). This is a process known as videoconferencing, as shown in
Figure 7.5.
Easier Backup
In business, data is extremely valuable, so making sure that employees
back up their data is critical. One way to address this problem is to keep all
valuable data on a shared storage device that employees access through a
network. Often the person managing the network has the responsibility of making
regular backups of the data on the shared storage device from a single, central
location. Network backup software is also available that enables backups to be
made of files stored on employees' hard drives. This way, the files do not have
to be copied to the central server to be backed up.
HOW NETWORKS ARE STRUCTURED
To understand the different types of networks and how they operate, it
important to know something about how networks can be structured. Fir there are
two main types of networks, distinguished mainly by geography local area
networks (LANs) and wide area networks (WANs). Second, any o these types can be
classified according to the logical relationships among the computers. There are
networks that use servers (such as file servers an, application servers) and
those that do not (called peer-to-peer networks).
Local Area Networks
A network of computers located relatively near each other and connected
b3 a cable (or a small radio transmitter) is a local area network (LAN). A LAN
can consist of just two or three PCs connected together to share resources, or
it can include several hundred computers of different kinds. Any network that
exists within a single building, or even a group of adjacent buildings, is considered
a LAN.
A LAN permits all the computers connected to it to share hardware, software,
and data. The most commonly shared resources are disk storage devices and
printers. To LAN users, the network is (or should be) completely transparent,
which means that the shared devices on it seem to be directly connected to the
user's computer as if they were merely peripherals. For example, a file server
should appear to the LAN user simply as another disk drive.
In addition to shared hardware, LANs can provide all the other benefits of
networks, including simultaneous access, enhanced personal communication, and
easier backup.
