Science and Technology^191
FIND OUT MORE. Computers 190 • Light 178–179 • Telecommunications 192–193
The global computer network, connecting computers
by telephone cables, optical fibres, and microwaves,
is called the Internet. The Internet provides almost
instant electronic communication around the world.
WHAT IS THE WORLD WIDE WEB?
The World Wide Web is a library of billions of pages
of information, including. SEARCH ENGINES,
stored on servers connected to the Internet. The pages
are written using hypertext, which links them.
A program called a browser on your computer uses
a web address (URL) to request a page. The request is
routed through the Internet to the correct server, and
the page is sent back to your computer.HOW DOES A SEARCH ENGINE RANK PAGES?
Entering the words “team sports” will produce
a list of millions of results from a search engine.
The engine tries to place the most relevant pages
at the top of the list. Different engines do this in
different ways. For example, the engine may check if
all the words appear or how many times they appear.HOW DOES THE INTERNET WORK?
Every computer linked to the Internet has an address.
This is its IP number. When you send a message or
request information on the Internet, your computer
sends packets of data with the sender’s and receiver’s
addresses attached. Special computers called servers
and routers direct the data through the Internet.WHAT IS THE TRAVELLING SALESMAN PROBLEM?
A network of roads connects the towns that a
travelling salesman must visit. How does he work out
the shortest route to take so that he visits each town
only once? This is a difficult mathematical puzzle.
The same problem faces engineers designing efficient
communications networks.WHAT IS HYPERTEXT?
Web pages are written using hypertext. Hypertext
links one web page to another. Web pages contain
text prepared in a computer language called HTML.
Hypertext links special words or phrases to other
sections of the document, or to other documents.
Clicking on a link takes you to the linked page.If you need to find information on the World Wide Web, you use
a program called a search engine. When you enter keywords, the
search engine (located on a server) makes a hypertext list of
web pages that have the words you are looking for.A network is formed when people, places, or things
are linked together. A rail network links towns and
cities. A computer network links computers.
USES FOR THE INTERNET 1
We are always finding new ways to use the Internet, from swapping
text messages between messenger programs to playing online computer
games. Video phone calls, shown above, are becoming popular, allowing
people to see and talk to each other over distances.FIND OUT MORE. Internet 191 • Telecommunications 192–193
4 FIBRE OPTICS
An optical fibre is a hair-thin
strand of pure glass. It carries
computer data as pulses of laser
light. Reflections stop the light
escaping through the fibre walls,
so it emerges at the end almost
as bright as when it went in.SEARCH ENGINES
4 NETWORK CONTROL
The global telephone system
is the largest communications
network on Earth. Engineers
at this telecommunications
control centre look after
network links and control the
flow of information.Internet
Networks
Optic fibre
directs light
along its
length by
internal
reflection
TIM BERNERS LEE
British, 1955-
MARC ANDREESSEN
American, 1971-
Tim Berners Lee invented the
World Wide Web as a source
of information for scientists in
the 1980s. In 1993, Marc
Andreessen developed the first
browser program (Mosaic)
with text, pictures, and
hypertext links.s
networks
?
ne.
Internet