a computer network serviced by a maintenance subsystem holds a control processing module holding a data path array as interface to a main memory module and i / o module . a maintenance controller in the cpm has a preloaded flash memory unit holding all the necessary operating addresses and data which can be rapidly transferred via a special wide parallel high speed data bus to a data path array unit for subsequent conveyance to a channel microcode block in a main memory module . the operating data include channel microcode data necessary for the i / o module to communicate with different types of peripheral devices .