The system of the present invention provides for the flow control of commands to devices connected through the system'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 "valid bits" 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.