Книга: Distributed operating systems

1.2.2. Advantages of Distributed Systems over Independent PCs

1.2.2. Advantages of Distributed Systems over Independent PCs

Given that microprocessors are a cost-effective way to do business, why not just give everyone his[1] own PC and let people work independently? For one thing, many users need to share data. For example, airline reservation clerks need access to the master data base of flights and existing reservations. Giving each clerk his own private copy of the entire data base would not work, since nobody would know which seats the other clerks had already sold. Shared data are absolutely essential to this and many other applications, so the machines must be interconnected. Interconnecting the machines leads to a distributed system.

Sharing often involves more than just data. Expensive peripherals, such as color laser printers, phototypesetters, and massive archival storage devices (e.g., optical jukeboxes), are also candidates.

A third reason to connect a group of isolated computers into a distributed system is to achieve enhanced person-to-person communication. For many people, electronic mail has numerous attractions over paper mail, telephone, and FAX. It is much faster than paper mail, does not require both parties to be available at the same time as does the telephone, and unlike FAX, produces documents that can be edited, rearranged, stored in the computer, and manipulated with text processing programs.

Finally, a distributed system is potentially more flexible than giving each user an isolated personal computer. Although one model is to give each person a personal computer and connect them all with a LAN, this is not the only possibility. Another one is to have a mixture of personal and shared computers, perhaps of different sizes, and let jobs run on the most appropriate one, rather than always on the owner's machine. In this way, the workload can be spread over the computers more effectively, and the loss of a few machines may be compensated for by letting people run their jobs elsewhere. Figure 1-2 summarizes these points.

Fig. 1-2. Advantages of distributed systems over isolated (personal) computers.

Оглавление книги