the system of the present invention provides for the flow control of commands to devices connected through the system &# 39 ; s memory management unit and is particularly useful in a multi - tasking computer system in which multiple processes access the same device . in the method and apparatus of the present invention , devices that are connected to the system through the mmu are controlled using the page fault mechanism of the mmu and the page fault handler in each segment . addresses are allocated in the process address space for each process to provide for the addressing of the devices and device queues connected through the mmu , such that one device or one device queue is mapped into one segment of each process address space that will access the device . the &# 34 ; valid bits &# 34 ; associated with each page in a segment are turned on / off by the process or operating system in order to control the device . if the valid bits are off or reset and an attempt is made to access at the address , a page fault occurs and the page fault mechanism invokes the page fault handler of the corresponding segment . the page fault mechanism of the mmu and the page fault handler of each segment are then utilized to determine the reason the page fault occurred with respect to a particular process and perform predetermining steps to control the flow of commands to the device .