Describing the major reasons for its growth and providing a brief history, this paper gives a synoptic view of a new computer sub-industry: independent, third-party computer maintenance and field support services. It details the major modes of delivery of maintenance and field support services now available to users and compares them to one another. The organization and the technical services provided by independent, third-party contracting firms are described. Particular attention is paid to

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... e special needs of mixedvendor computer system users. BACKGROUND In the early days of the computer industry, user needs for system maintenance and field service support was not a matter of particular emphasis. The few large manufacturers each took pride in the service reliability of their products, and it was this aspect, and not the need for maintenance and field service, which was stressed. In addition, virtually all early systems were supplied by a single vendor. The vendor-manufacturer provided maintenance and field sup-l}QxLW-vic.es, thr.Quglt.Ws.Qwn _s~n:is;~< QJ.gal}iz.atiQI),> whi~h, in most cases, was adequately distributed geographically. The end-user, then, had a convenient single source to meet his maintenance and field support needs. This basic situation began to change with the advent of plug-compatible equipment and the resulting proliferation of mixed-vendor systems. User requirements became more complex. And no longer could the end-user rely upon a single source to meet these requirements for all elements in his system. At first, his only course of action was to contract with the service organizations of each manufacturer whose equipment he used. Compounding the situation was the entering into the field of numerous small manufacturers. While offering excellent products, many could not establish and maintain the extensive service networks needed to serve users dispersed nationwide or even worldwide. In order for these smatter manufacturers to market their products over larger geographic areas·, they, too, needed a way of providing mainte-