Question

Describe how direct memory access (DMA) works and explain why DMA requires cycle stealing.

Answer 1

DMA or the direct memory access is nothing but a means of having the peripheral device control a processor's memory bus directly. DMA actually permits the peripherals to transfer the data directly to or from memory without having each byte handled by the processor. When the CPU is using the programmed I/O it occupies for the entire duration of the read/write operation and thus unable to perform the other functionalities. With the help of DMA, the CPU first initializes the transfer and then it performs other operations while the transfer is in the progress.and it finally receives interrupt signal from the DMA controller when the operation is executed properly. Sometimes, DMA is also being used for the memory to memory copying or even moving the data within the memory.

The DMA module make use of the system bus only when the processor does not require it, or it might force the processor to suspend the operation though temporarily. The latter technique is quite common and is referred as the cycle stealing.because the DMA module in function steals the bus cycle.