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Evolution of Distributed Computing
In distributed computing, an application is divided into smaller parts that run simultane-
ously on different computers. This is also referred to as network computing because the
smaller parts communicate over the network generally using protocols built on top of
TCP/IP or UDP. The smaller application parts are called tiers . Each tier provides an inde-
pendent set of services that can be consumed by the connecting or client tier. The tiers
can be further divided into layers , which provide granular-level functions. Most applica-
tions have three distinct layers:
• The presentation layer is responsible for the user interfaces.
• The business layer executes the business rules. In the process, it also interacts with
the data access layer.
• The data access layer is responsible retrieving and manipulating data stored in
enterprise information systems (EISs).
The modern state of network computing can be better understood by analyzing the
gradual transition of distributed application architecture. In the next few sections, I will
examine the transition of distributed architecture with suitable examples.
Single-Tier Architecture
The single-tier architecture dates back to the days of monolithic mainframes connected
by dumb terminals. The entire application comprising layers such as user interfaces,
business rules, and data was collocated on the same physical host. The users interacted
with these systems using terminals or consoles, which had very limited text-based pro-
cessing capabilities (see Figure 1-1).
Figure 1-1. Single-tier architecture
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