essage control functions, permitting the central processing unit and the user appli- cation programs to treat the communications network as just an- other high-speed, on-line peripheral device. Because the front-end processor is essentially a programmable computer, it can be pro- grammed to perform an almost limitless variety of functions. But in its role as external controller of a centralized data communications network, the specific functions generally programmed are those that relate to data and message control. 3.13.1 Selection and Evaluation Front-end processors deserve careful investigation because of their many apparent advantages over hard-wired communications con- trollers. Such investigations should include as many probing ques- 50 TELECOMMUNICATIONS tions as possible, because there are potentially serious pitfalls to be avoided. One potential problem is the question of overloading the front- end processor, with the resultant loss of data. Sophisticated data and message control programs will consume large quantities of the front- end processor's computing and memory facilities, just as they do in a centrally-based communications system. Since many front-end processors are based on minicomputers, the possibility of overload- ing is all the more real. A tendency toward overloading can easily negate any apparent advantages of expandability and growth poten- tial. Another serious question is that of software. The body of software required for terminal control, line control, and message control ac- tivities, not to mention application-oriented pre-processing, is un- questionably complex. It is also vital to the operation of these systems. The prospective user must determine whether or not the supplier is capable of supplying this software, at what level of com- pleteness, with what assurance of bugfree stability, with what chances of interfacing smoothly with the central system software, and with how much installation assistance. Another buyer's tip is to look for the word "turnkey." Turnkey installation of