In my opinion, there is no single `best` online service. The

choice depends on your 1......... (prltacuair) needs and prefe-

rences. Most users have their own 2....... (ftrvaioue), but this

can prevent them from seeing the 3........ (agtvndaaes) of other

services. Each one offers something which is either 4........

(unique) to that service, or which is 5........ (bteetr) than the

same features on other services. So, when considering an online

service, decide whether its features 6....... (cosrernopd) to

what you need. Until all services are 7........ (iilktneernd),

most of us will need to 8.......... (cunoitne) using more than

one.

Task 4

1 Do you yhink the English in the text is:

a formal ?

b neutral ?

c informal ?

2 Do you think this article originally appeared in :

a a computer magazine ?

b a general magazine for young people ?

c a general magazine for adults ?

d an online bulletin board ?

e the science page of a newspaper ?

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Give reasons for your choice.

Task 5

Make these words negative by adding the appropriate prefix

from those given below. The first one has been done for you.

in- un- im- dis-

1 infrequently

2 ...loyal

3 ...advantages

4 ...specific

5 ...like

6 ...real

7 ...probably

8 ...available

Task 6

Match each word or expression in the first column with a sy-

nonym in the second column.

1 but a ultimately

2 while b however

3 still c whereas

4 for my part d nevertheless

5 eventually e personally

6 until then f meanwhile

Task 8

Using the information in the text below, explain the origin

of the word modem.

Analog transmission

The older telephone systems function on the basis of analog

signals representing voice modulation patterns which are repre-

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sented by variations in wave forms. When using telephone lines

for transmitting data by terminal to a computer, the digital sig-

nals from the terminal need to be converted to analog signals by

an acoustic coupler or modem prior to transmission. A modem is a

device which serves a dual purpose because it acts as a MOdulator

(digital to analog) and DEModulator (analog to digital), hence

the name MODEM. An analog communication system requires a modem

at either end of the communication line. When the signals are re-

ceived by the distant computer, the signals are reconverted to

digital form prior to being input for processing.

Task 9

Before reading the text below, answer these questions.

1 What are the advantages of digital transmission ?

2 How does digital transmission differ from analog transmission ?

3 What information does the code supply ?

Now read the text to check your answers.

Digital transmission

Analog transmission has been in use for many years as the

vasis of telephone technology and is very effective for this pur-

pose, but it is not so suitable for high-speed transmission of

information. Digital transmission consists of electrical pulses

representing data in binary code as a series of on/off pulses. A

number of different codes exist, some of which are based on a 6-,

7-, or 8-bit structure. ASCII is a 7-bit code and EBCDIC is an

8-bit code. The codes represent characters, transmission control

signals, information separators, and device control. Digital

technology has a number of advantages compared to analog, inclu-

ding higher transmission speed, lower incidence of errors, and

the facility for mixing data consisting of voice, image, and text

on the same circuit. It is for this reason that data transmissi-

ons will be increasingly digital in the future. A network struc-

ture known as Integrated Services Digital Network (ISDN) facili-

tates these aspects.

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Quiz

Unit 9 (Online services)

1 What do you call an agreement that covers the procedures used

to exchange information between co-operating computers ?

2 What kind of transmission has been the basis for telephone

technology for many years, though it is gradually being repla-

ced ?

3 What kind of transmission consists of electrical signals repre-

senting data in binary code ?

4 What name is given to a public database that can be accessed

over a computer on telephone network ?

5 A ........ controller controls a number of similar peripheral

devices such as terminals and links them to the main computer.

6 What merges information from several channels to one channel ?

7 What do you call a device that converts the computers digital

bit stream into an analog signal for transmission over a telep-

hone line ?

8 What term is used to name the process of sending signals elect-

ronically ?

9 To send programs or data from a central computer to a remote PS

is ..........

10 What do you call single vibrations of electric current ?

UNIT 10

COMPUTER NETWORK

Task 1

Try to answer these questions.

1 What is a LAN ?

2 What is a WAN ?

3 What is a distributed system ?

Task 2

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Before reading the text, match these words and phrases with

their definitions.

1 protocol a analyse the syntax of a string of input sym-

bols

2 bulletin board b a teleconferencing system allowing users to

read messages left by other users

3 user interface c agreement governing the procedures used to

exchange information between co-operating

computers

4 make a query d means of communication between a human user

and a computer system

5 parse e taking place at exactly the same time as

something else

6 synchronous f request a search

Task 3

Read quickly through the text below, then match each parag-

raph with the appropriate summary.

a Network uses, past and present

b How distributed systems work

c Networks and the future

d What networks are and how they

‘OMPUTER NETWORKS

Computer networks link computers by communication lines and

software protocols,allowing data to be exchanged rapidly and re-

liably. Traditionally, networks have been split between wide area

networks (WANs) and local area networks (LANs). A WAN is a net-

work connected over longdistance telephone lines,and a LAN is a

localised network usually in one building or a group of buildings

close together. The distinction,however,is becoming blurred. It

is now possible to connect up LANs remotely over telephone links

so that they look as though they are a single LAN.

Originally, networks were used to provide terminal access to

another computer and to transfer files between computers. To-

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day,networks carry e-mail, provide access to public databases and

bulletin boards,and are beginning to be used for distributed sys-

tems. Networks also allow users in one locality to share expensi-

ve resources,such as printers and disk-systems.

Distributed computer systems are built using networked com-

puters that co-operate to perform tasks. In this environment each

part of the networked system does what it is best at. The

high-quality bit-mapped graphics screen of a personal computer or

workstation provides a good user interface. The mainframe, on the

other hand, can handle large numbers of queries and return the

results to the users. In a distributed environment, a user might

use his PC to make a query against a central database. The PC

passes the query, written in a special language (e.g. Structured

Query Language - SQL), to the mainframe, which then parses the

query, returning to the user only the data requested. The user

might then use his PC to draw graphs based on the data. By pas-

sing back to the user`s PC only the specific information reques-

ted, network traffic is reduced. If the whole file were transmit-

ted, the PC would then have to perform the query itself, reducing

the efficiency of both network and PC.