Computers and peripherals (pieces or
equipment that are connected to the central
processing unit of a computer system)
connected together form a network. Networks
allow communication between computers and
the sharing of hardware (such as printers)
and software (programs and data). A network
that covers a small area e.g. an office or
building is known as a LAN (local area
network). The main computers that provide
services on the network are called servers
e.g. a file server provides a central storage
area for data files. The computers that use the
services are known as clients. The computers
can be connected using various types of
cabling, including the ordinary telephone
system wiring. A main data communications
cable connecting LANs together is referred to
as a backbone. Various electronic devices are
also used to amplify, filter and determine the
best path for the signals These include
bridges for dividing a LAN into separate parts
or connecting similar networks together.
gateways for connecting different types of
networks and routers for connecting different
networks together and determining the best
path (or route) for the signals. Routers are
used to connect networks to form the
Internet. A modern (modulator/demodulator)
is used to convert signals from analogue
(having a variety of levels) to digital (having
only two levels, representing on and off) for
connection to the ordinary telephone system.
Alternatively, an ISDN Gntegrated services
digital network) adapter or a DSL (digital
subscriber line) modern can be used to allow
digital signals to be used without being
converted to analogue signals.

There are different standard methods of
connecting computers in a LAN. One of the
most common is known as Ethernet. Each
computer must have a network adapter
(special electronics to control the network
connection). This is usually in the form of an
expansion card known as a network interface
card (NIC). All the computers are connected
through another electronic device known as a
hub. The electronics in the hub are used to
amplify the signals to prevent them from
becoming too weak before they reach the
desired computer. The cable normally used to
connect the computers to the hub is known as
twisted-pair cabling. It contains two cables
twisted together to eliminate interference
from external signals. In a home network, the
mains power cables built into the house can
be used instead it electronic devices called
isolation adapters are used to isolate the
computer from the mains electricity running
through the cable. In future, wireless
networks will use a radio transmitter and
receiver turned to use the same radio
frequency, instead of cabling.

In a client/server network. the main
server computer provides the services
(sharing of printers. programs or data. etc.)
and the attached client computers can be
normal computers or simple terminals.
Terminals require the server to do most or all
of the processing. A thin client (or thin
terminal), such as a NetPC, has a processor
that does some of the processing but a dumb
terminal does not have a processor and all
the processing must be done by the server
computer.

One character oi data is reierred to in
computing as a byte. in the binary system (a
number system that only uses two digits Le. 1
and 0) used in computers. a byte is made up
of 8 bits where a bit is a 1 or a 0. When data
is transmitted through a network system. it
can be transmitted in different ways.
Asynchronous transmission (or slopstart
transmission) sends the data one byte (or
character) at a time. A start bit (called a
control bit) is added to indicate the beginning
of each byte and another control bit called a
stop bit is added to indicate the end of each
byte. Synchronous transmission sends the
data in blocks. Extra bytes of data called
synch bytes are added at the beginning and
end of each block. They are used to
synchronise the sending and receiving
devices.

When a message is transmitted through a
network, it is processed in various ways by
the software and the hardware. It is first
processed by the applications program e.g. an
email program, and then it is processed by
the operating system. It is then processed by
the hardware such as the network interface
card and finally by the network electronics
e.g. a router, as it passes through the network
system. When it arrives at its destination, it is
similarly processed in reverse order to display
the message on the display screen of the
receiving computer.