There has traditionally been a distinction between minicomputers and their more powerful cousins, mainframes, but this distinction has faded as minicomputers have increased in power and capabilities. One enduring distinction between these two has been the concept of the Front End Processor (FEP). In order to offload the tasks of servicing terminal I/O and other forms of communication, most mainframes have a system connected to the main processor by means of a high-speed bus that is dedicated to managing communications. With this arrangement, terminals communicate with the FEP, rather than directly with the mainframe.

As local area networking has become more common, it has changed the way terminals are attached to host systems. Terminal concentrators are devices that exist as nodes on a network, and permit multiple terminal connections, that are then multiplexed together, and sent down the network to the host system through its network interface. PCs can also function in the same way as these concentrators, exchanging terminal traffic directly across the network, rather than a dedicated direct connection.

What does it do?
Host systems are the traditional computing engines of corporate America. Originally handling all the computing requirements of the enterprise, they have gradually been off-loaded by the developing capabilities of the PC and PC LANs. The first wave of migration included most common office automation applications, such as word processing and spreadsheets. PC LANs provided the ability to downsize electronic mail applications, as well as file sharing and print sharing services.

Databases, transaction processing systems, and process control applications are among those that have moved much more slowly. These applications are often custom-written at great expense, require the security and reliability associated with a mainframe system, and may require response to real-time events, which is not a strength of PC architectures.

How is it used?
The future of host systems is a much-debated issue. There is a clear motivation to move away from costly, proprietary host environments. However, the investments that have been made in these systems often make the decision to downsize a complex one. The security and reliability of host operating systems have only been recently developed for PC LAN environments, and the processing power of PCs has increased so rapidly many corporations are not ready to bet the business on a PC-based architecture.

Many initiatives in the areas of client/server computing, developments in PC server architecture such as redundant disk arrays, and PC network operating system enhancements have been driven by the demands of those applications that have resisted migration away from the mainframe. Some contemporary LAN designs stress the use of server farms in which all file servers, rather than being dispersed among the workgroups that use them, are centralized in one location for ease of control and support.

Ironically, many of the recent developments in PC, and, particularly, PC LAN technology are relatively old concepts in host system architecture, and combine to make the future of PC distributed computing look a lot like the host environments, without the big iron or the proprietary restrictions.

Where do I get more information?
Contact your local CBV Office.