In DMA transfer, the DMA controller sends a DMA request to the CPU, in response to which CPU puts all its address, data and control bus lines in the high impedance states. The DMA controller can then transfer data directly between device and memory without CPU intervention.

What happens during DMA transfer?

Once the DMA controller is granted access to the system bus by the CPU, it transfers all bytes of data in the data block before releasing control of the system buses back to the CPU, but renders the CPU inactive for relatively long periods of time. The mode is also called “Block Transfer Mode”.

What is DMA transfer?

Stands for "Direct Memory Access." DMA is a method of transferring data from the computer's RAM to another part of the computer without processing it using the CPU. ... Ultra DMA hard drives use DMA to transfer data faster than previous hard drives that required the data to first be run through the CPU.