A maintenance processor forms part of a computer network wherein the processor (also designated as the User Interface Processor) operates to initialize and maintain and communicate to remote diagnostic terminals for purposes of confirming integrity of the system and also for displaying data for locating any faults or problems in the network. The maintenance subsystem initiates start-up and self-test routines in a sequenced order for establishing the integrity of the units in the network. The subsystem includes means for testing two types of subsystems, that is, one having I/O controllers with self-test capability and another subsystem having I/O controllers without self-test capability. The UIP provides means for complete control of the network. It can interface the network to a remote service center where all operations such as power-up and initialization can be also effectuated.