Direct memory access(DMA) is a method which enables an input/output (I/O) device that is used to receive and send data directly from the main memory, to speed up the memory operations and bypass the CPU. The entire gamut is managed by a chip called DMA controller (DMAC).
Without the presence of DMA, in some instances of CPU is using programmed input/output and is actually occupied for duration of write and read operation and that is the reason it is available to perform other vital tasks. Many of the hardware systems use DMA, including sound cards, network cards, disk drive controllers and graphic cards. In multi-core processors, DMA is used for intra-chip data transfer. DMA can be used for moving data within memory or for "memory to memory".