Learning DCOM

Distributed Computing Using RPC

In a three-tier environment such as the one shown in Figure 1-4, software developers distributed responsibility among each participant. They took away some intelligence from the clients, in a way that clients would act only as a front-end. In other words, clients were responsible for simply displaying, capturing, and validating user data. From this, a new terminology came into existence. The term “thin client” was used to represent the first tier in a three-tier system. PCs that ran these clients did not need to be high-end. These first-tier clients would communicate with the middle-tier servers via a remoting standard, remote procedure calls (RPC), to be discussed in a moment.

Figure 1-4. Three-tier technology

The middle tier was a server tier that supported complex business processing (e.g., calculate expense and calculate factorials) for its clients. Most of the performance problems found on the client end in the client/server scenario had now been relocated to this second tier. Therefore, the middle tier had to be powerful and smart. It had to be a high-end computer, running operating systems such as Windows NT or Solaris, with multiple CPUs to take advantage of symmetric multiprocessing. These middle-tier servers would communicate with the back-end third tier, again using the RPC standard.^[1] The third-tier, back-end servers managed persistent business ...