Question on input/output


in virtually all systems that include DMA modules,DMA access to main memory is given higher priority than CPU access to main memory.why?


If a processor is held up in attempting to read or write memory, usually no damage occurs except a slight loss of time. However, a DMA transfer may be to or from a device that is receiving or sending data in a stream (e.g., disk or network), and cannot be stopped. Thus, if the DMA module is held up (denied continuing access to main memory), data will be lost.