A personal computer system that is assembled from components selected by the end-user; it may be assembled by the end user or a system builder. The advantage of custom assembly is the components can be selected to match the user's application. Manufacturer options of mass-produced computers may not meet the specific requirements of an end user. Since a wide range of standardized low-cost interchangeable hardware is available. A system builder specializes in customized or special purpose systems, which cannot be obtained off-the-shelf from major manufacturers.