Q. Explain working of Direct Memory Access?

In both programmed I/O and interrupt-driven processor is busy with executing input/output instructions and I/O transfer rate is limited by speed with which processor can test and service a device. What about a scheme that needs minimal intervention of CPU for input/output? These two types of shortcomings can be overcome with a more efficient technique called as DMA that behaves as if it has taken over control from processor.  C  Consequently the question is: why do we employ DMA interface? It is employed primarily when a large amount of data is to be transferred from I/O device to Memory.