DMA Explained Simply

Normally, when we have an I/O device like a network card, if we want to transfer data, the CPU copies the data byte by byte from the device to RAM. That’s not very efficient, because the CPU could be doing more useful work — copying data from an I/O device to memory is a simple repetitive task.

That’s where DMA (Direct Memory Access) comes in. It’s a hardware component (an electronic circuit) that can transfer data directly between an I/O device and memory (RAM or disk) without the CPU being involved in every byte.

The CPU only needs to set things up: it tells the DMA where to put the data (buffers, memory addresses, size, etc.), then the DMA takes over the transfer. When the transfer is complete, the DMA sends a single interrupt to the CPU to say “transfer done.”

This is much more efficient and generates far fewer interrupts, freeing the CPU to do other work.

The DMA can either be a separate chip on the motherboard or integrated into the I/O device itself (like modern network cards or disk controllers).