metropolitan-area networks MANs): A data network designed
for a town or city.
home-area networks (HANs): A network contained within a
user's home that connects a person's digital devices.
In addition to these types, the following characteristics are also used to categorize
different types of networks:
topology : The geometric arrangement of a computer system. Common
topologies include a bus, star, and ring..
protocol : The protocol defines a common set of rules and signals that
computers on the network use to communicate. One of the most popular
protocols for LANs is called Ethernet. Another popular LAN protocol
for PCs is the IBM token-ring network .
architecture : Networks can be broadly classified as using either a peer-topeer or client/server architecture.
Computers on a network are sometimes called nodes. Computers
and devices that allocate resources for a network are called servers.
The meaning of the term computer security has evolved in recent years. Before
the problem of data security became widely publicized in the media, most people‟s
idea of computer security focused on the physical machine. Traditionally,
computer facilities have been physically protected for three reasons:
To prevent theft of or damage to the hardware
To prevent theft of or damage to the information
To prevent disruption of service
Strict procedures for access to the machine room are used by most
organizations, and these procedures are often an organization‟s only obvious
computer security measures. Today, however, with pervasive remote terminal
access, communications, and networking, physical measures rarely provide
meaningful protection for either the information or the service; only the
hardware is secure. Nonetheless, most computer facilities continue to protect
their physical machine far better than they do their data, even when the value
of the data is several times greater than the value of the hardware.