In the early days of data communications information traveled along a single, well-defined route from the remote computer to the host. The reason for this was that the remote computer was fairly restricted in its computing and data-storage capabilities and so the serious computing was carried out at the data center. Most large organizations have retained their large data-processing centers but have changed emphasis on the use to which they are put. They are now used for batch processing of data where either the volume is too large to be processed by the remote systems or the processing itself is not time-critical or as large repositories for files so that the files can be accessed and changed by a number of microcomputers. The advent of very powerful microcomputers (some much more powerful than earlier mainframes), coupled with the marked increase in the reliability and speed of networks, has moved much of the data processing out to the world of the user onto the shop floor, into the laboratory, within an office department, and even to individuals on the desks in their own homes.
In the automobile industry, for example, the European headquarters of a U.S. corporation would have its own designs and engineering department with a computer capable of processing, displaying, and printing design calculations. However, it may still require access to the larger U.S. machines for more complex applications requiring greater computer power, particularly for the modeling of designs that can be very CPU intensive. In addition, there may be a number of test units, testing engines, and transmissions, each controlled by its own micro and supervised by a host machine. If there is a similar engineering department in, for example, Germany, it may be useful to collect and compare statistical data from test results. Also, since people must be paid, it may be useful to have a link with the mainframe computer in the data center for the processing of payroll records. The demand for the linking of computers and the sharing of information and resources is increasing constantly. This has led to the advent of a data communications network (usually just called a network).