NonStop Systems Introduction

The Application Server Environment
NonStop Systems Introduction— 527825-001
3-6
Multi-Tiered Architectures
As you will see later, the terms client and server are relative. A server that receives a
request from a client can then make a request of another server and, in effect, then
becomes a client of that server.
The client/server structure made it possible for applications to handle varying
workloads and grow in transaction processing capacity as the number of clients
increased. This architecture forms the basis for the application server environments
described later in this section.
Multi-Tiered Architectures
The previous example shows what is known as a two-tiered architecture, consisting of
a presentation layer and business application layer. Using current technologies,
client/server architectures consisting of multiple tiers (called N-tiered architectures) are
possible. Figure 3-4 on page 3-7 shows an example of a three-tiered architecture that
further distributes the activities involved in a transaction by separating the GUI used for
data entry from the business logic, and the business logic from the logic that provides
access to the database. Typically, on Nonstop systems, tiers two and three run on the
same host computer, although, as the figure shows, they can be hosted on different
computers.