When the process requests for a DMA transfer

Answer: process is temporarily suspended & another process gets executed

Direct memory access (DMA) is a technique that allows an input/output (I/O) device to send to or receive data directly from the main memory, bypassing the CPU to speed up memory operations.

With DMA, the CPU can process other tasks while data transfer is being performed. The transfer of data is first initiated by the CPU.

DMA controller (DMAC) is a control unit, part of I/O device’s interface circuit, which can transfer blocks of data between I/O devices and main memory with minimal intervention from the processor.

The process requesting the DMA transfer is paused and the operation is performed, meanwhile another process is run on the processor.

The data can be transferred to and from memory by the DMAC in three ways.

In burst mode, the system bus is released only after the data transfer is completed.

In cycle stealing mode, during the transfer of data between the DMA channel and I/O device, the system bus is relinquished for a few clock cycles so that the CPU can perform other tasks. When the data transfer is complete, the CPU receives an interrupt request from the DMA controller.

In transparent mode, the DMAC can take charge of the system bus only when it is not required by the processor.