DMA

Direct Memory Access (DMA) is a feature of computer architectures that allows peripheral devices to read from and write to main memory without continuous CPU intervention. By moving data directly between memory and a device, DMA reduces the workload on the processor and can significantly increase data transfer throughput for I/O heavy operations such as disk I/O, networking, and audio or video streaming.

In operation, a DMA-capable device or a dedicated DMA controller coordinates a transfer. The CPU configures the transfer by selecting a DMA channel and programming registers with the source and destination addresses, the transfer size, and the direction of data flow. When the transfer is ready, the DMA controller requests control of the system bus. After gaining bus access, it performs the data movement, freeing the CPU to perform other tasks. Upon completion, the DMA controller typically signals the CPU via an interrupt or a status flag.

DMA supports several transfer modes. Burst or block transfers use the bus aggressively for a contiguous block of data, while cycle stealing transfers take bus cycles intermittently, allowing the CPU to continue executing other instructions. Modern systems may also employ more advanced DMA engines with features such as chained or scatter-gather transfers and direct memory access without CPU intervention for long sequences.

In contemporary architectures, DMA functionality is often integrated into chipsets, peripherals, or PCI/PCIe devices, and may be protected by hardware support such as an IOMMU to ensure memory safety and address translation. DMA remains essential for high‑performance I/O, enabling faster data movement while freeing the CPU to handle computation and control tasks.