0195136047.pdf

320 DIGITAL BUILDING BLOCKS AND COMPUTER SYSTEMS

means of communicating between the computer and the outside world with external devices such

as oscilloscopes, data collection devices, and display devices. Most present-daydata acquisition

systems are designed to be compatible with microprocessors for processing the measured data.

A typical data acquisition and processing system is illustrated in Figure 6.3.3.

Amplification

Input signalsTransducers

Displays

Multiplexer

Reference

Analog-to-digital

converter

Display

Storage

Control

Mainframe

computer

Micro-

processor

Figure 6.3.3Block diagram of typical data acquisition and processing system.

6.4 Computer Networks

Computer communications networksare the outcome of a combination of computers and telecom-

munication products. An interconnected group of independent computers and peripheral devices

that communicate with each other for the purpose of sharing software and hardware resources

is known as a computer communications network. Alocal-area network(LAN) is any physical

network technology that operates at high speed (usually tens of Mbits per second through several

Gbits per second) over short distances (up to a few thousand meters). Examples include Ethernet

and proNET-10. The stations, also known asnodes, within a LAN are physically linked with

each other through twisted pairs of copper wires, coaxial cables, or fiber-optic cables. Awide-

area network(WAN, also known aslong-haul network) is any physical network that spans large

geographic distances, usually operates at slower speeds, and has significantly higher delays than

a LAN. Stations within a WAN communicate with each other through standard telephone lines,

dedicated telephone lines, line-of-sight microwave systems, or fiber-optic links.Public-data

network(PDN) is network service offered by a common carrier, such as Telnet, Tymnet, and

Dataphone Digital Services of AT&T. ARPANET (Advanced Research Projects Agency of the

U.S. Department of Defense) is an example of a private communications network. CYBERNET

is an example of a remote-access communications network that provides access to huge databases

for their users in different countries. TheInternetis a collection of networks and gateways (special-

purpose dedicated computers attached to various networks routing packets of information from one

to the other), including the Milnet (military network) and NSFNET (National Science Foundation

network), that function as a single, cooperative virtual network providing universal connectivity

and application-level services such as theelectronic mail. The Internet reaches many universities,

government research labs, and military installations in several countries.

The future scope of the Internet, along with the World Wide Web (born in 1990), and the

commercialization of the Internet are bound to grow exponentially. In 1991, the U.S. Congress

passed the High Performance Computing Act to establish the National Research and Education

Network (NREN), which allows the electronic transfer of the entire Encyclopedia Britannica in

one second. Computer networks worldwide will feature 3–D animated graphics, radio and cellular

phone-links to portable computers, as well as fax, voice, and high-definition television. While the

Web is fast becoming a part of our everyday lives, the real Internet of the future may bear very

little resemblance to today’s plans.