NonStop Systems Introduction

The Application Server Environment
NonStop Systems Introduction— 527825-001
3-4
Client/Server Architecture
The earliest transaction processing environment was based on an architecture known
as requester-server, in which requester processes made requests of server
processes. A requester process is conceptually similar to the familiar client process
used in today’s architectures, except that the requester resides on the NonStop host
rather than on a workstation. In this arrangement, transactions originate from data-
entry terminals.
The requester-server architecture was implemented using the Pathway product. In this
model, data entry terminals were managed by a Terminal Control Process (TCP).
Requester programs, which performed screen presentation services, were written
using the SCREEN COBOL language. Pathway server modules performed the
database access functions. Figure 3-2 on page 3-4 illustrates the Pathway requester-
server model.
This model took advantage of multiple processors because in an application consisting
of multiple Pathway servers, the servers could run in different processors, and all could
process requests at the same time. It also allowed for application expansion by adding
copies of servers (known as a server class) to handle the additional demand. Pathway
processes would handle the additional communication paths between requesters and
servers. The concept of multiple server processes running on different processors is
known as distributed processing.
Client/Server Architecture
The next step in the evolution of application servers was based on the client/server
concept. In this now-familiar design, processing is separated into database-oriented
(server) and workstation-oriented (client) functions. Whereas the input devices used in
the early requester-server model were mainly data-entry terminals with no processing
power of their own, the client/server architectures are designed to take advantage of
Figure 3-2. Pathway Requester-Server Model
Requester Server
Server:
• Performs database-oriented
functions
• Provides information service
to user
Requester:
• Performs workstation-oriented
functions
• Requests information on
user's behalf
VST017.vsd
Host computer
Data entry terminal