Abstract: A computer system with provision for inserting/removing memory cartridges is improved by inhibiting erroneous operation as a result of noise produced on insertion/removal of a memory cartridge. Removable cartridges are connected/disconnected from a cartridge bus which is distinct from the system bus to which all other components are coupled. A controlled isolation is provided between the two buses. An idler routine ensures that in the absence of operator requested tasks the isolation prevents noise on the cartridge bus from reaching the system bus. When the processor executes an instruction (or only selected instructions) the isolation is disabled so that data/instructions can flow to/from the system and cartridge bus.