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Chapter 5 IT Infrastructure and Emerging Technologies 199

PCs in the world, and 300 million new PCs are sold each year. 90% are thought
to run a version of Windows, and 10% run a Macintosh OS. The Wintel domi-
nance as a computing platform is receding as iPhone and Android device sales
increase. Nearly one billion people worldwide own smartphones, and most of
these users access the Internet with their mobile devices.
Proliferation of PCs in the 1980s and early 1990s launched a spate of personal
desktop productivity software tools—word processors, spreadsheets, electronic
presentation software, and small data management programs—that were very
valuable to both home and corporate users. These PCs were stand-alone systems
until PC operating system software in the 1990s made it possible to link them
into networks.

Client/Server Era (1983 to Present)
In client/server computing, desktop or laptop computers called clients are
networked to powerful server computers that provide the client computers
with a variety of services and capabilities. Computer processing work is split
between these two types of machines. The client is the user point of entry,
whereas the server typically processes and stores shared data, serves up Web
pages, or manages network activities. The term “server” refers to both the soft-
ware application and the physical computer on which the network software
runs. The server could be a mainframe, but today, server computers typically
are more powerful versions of personal computers, based on inexpensive chips
and often using multiple processors in a single computer box., or in server
racks.
The simplest client/server network consists of a client computer
networked to a server computer, with processing split between the two types
of machines. This is called a two-tiered client/server architecture. Whereas
simple client/server networks can be found in small businesses, most cor-
porations have more complex, multitiered (often called N-tier) client/
server architectures in which the work of the entire network is balanced
over several different levels of servers, depending on the kind of service being
requested (see Figure 5.3).
For instance, at the first level, a Web server will serve a Web page to a
client in response to a request for service. Web server software is responsible

FIGURE 5.3 A MULTITIERED CLIENT/SERVER NETWORK (N-TIER)

In a multitiered client/server network, client requests for service are handled by different levels of
servers.

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