Direct Memory Access (DMA)

This is a method where the devices can directly transfer data to and from main memory without CPU moving each byte.

Programmed IO (PIO)

This is the regular way of copying data from memory to device. Where every byte goes via CPU.

How it works

1. CPU tells the device about the memory address and length.
2. Device’s DMA controller moves the data on the system bus directly to/from RAM.
3. CPU is free to do other work during transfer.