The traditional architecture for multi-user systems was teleprocessing, where there is one
computer with a single central processing unit (CPU) and a number of terminals, as
illustrated in Figure 2.10. All processing is performed within the boundaries of the same
physical computer. User terminals are typically ‘dumb’ ones, incapable of functioning on
their own. They are cabled to the central computer. The terminals send messages via the
communications control subsystem of the operating system to the user’s application program,
which in turn uses the services of the DBMS. In the same way, messages are routed
back to the user’s terminal. Unfortunately, this architecture placed a tremendous burden
on the central computer, which not only had to run the application programs and the
DBMS, but also had to carry out a significant amount of work on behalf of the terminals
(such as formatting data for display on the screen).
In recent years, there have been significant advances in the development of highperformance
personal computers and networks. There is now an identifiable trend in
industry towards downsizing, that is, replacing expensive mainframe computers with
more cost-effective networks of personal computers that achieve the same, or even better,
results. This trend has given rise to the next two architectures: file-server and client–server.