HTML and CSS Reference
The Internet is an interconnected network of computer networks that is globally avail-
able. When an organization needs the communication capabilities of the Internet but
doesn't want its information to be available to everyone, either an intranet or extranet
An intranet is a private network that is contained within an organization or business.
Its purpose is to share organizational information and resources among coworkers.
When an intranet connects to the outside Internet, usually a gateway or firewall pro-
tects the intranet from unauthorized access.
An extranet is a private network that securely shares part of an organization's informa-
tion or operations with external partners such as suppliers, vendors, and customers.
Extranets can be used to exchange data, share information exclusively with business
partners, and collaborate with other organizations. Privacy and security are important
issues in extranet use. Digital certificates, encryption of messages, and virtual private
networks (VPNs) are some technologies used to provide privacy and security for an
extranet. Digital certificates and encryption used in e-commerce are discussed in
Recall that the original Internet—the ARPAnet—began with four hosts. The number of
host computers connected to the Internet grew each year. However, the communication
was text-based and the information stored on computers connected to the Internet was
not easy to obtain. Initially, the use of the Internet was limited to academics,
researchers, students, and government employees. Even with these restrictions there
were over 300,000 hosts in 1990.
Why did the Internet grow from 300,000 hosts in 1990 to over 109 million in just over
a decade? In the early 1990s, the convergence of three events occurred to cause explo-
sive growth of the Internet.
In 1991, the NSFnet removed the restriction on commercial use of the Internet, setting
the stage for future electronic commerce. Businesses were now welcome on the Internet.
However, while businesses were no longer banned, the Internet was still text-based and
not easy to use. The next developments solved this issue.
While working at CERN, a research facility in Switzerland, Tim Berners-Lee envisioned
a means of communication for scientists where they could easily “hyperlink” to another
research paper or article and immediately view it. Berners-Lee created the World Wide
Web to fulfill this need and in 1991 he posted the code in a newsgroup. This version of
the World Wide Web used Hypertext Transfer Protocol (HTTP) to communicate
between the client computer and the Web server, used Hypertext Markup Language
(HTML) to format the documents, and was text-based.
In 1993, the first graphics-based Web browser, Mosaic, became available. Marc
Andreessen and graduate students working at the National Center for Supercomputing
Applications (NCSA) at the University of Illinois Urbana-Champaign developed Mosaic.
Some individuals in this group later created another well-known Web browser—