Direct Memory Access (DMA)
If we look at the computer system diagram we can see that when transferring data from a device such as a hard disk the CPU is heavily involved.
Each word of data has to be transferred from the disk, through the CPU and individually placed into memory. This places a heavy burden on the CPU and stops it from performing any useful tasks.
To address this problem we use a system of Direct Memory Access (DMA).
Next: Implementing DMA