Direct Memory Access
Usually the only component that accesses directly the system RAM memory is the processor. With DMA feature any other component can access the system RAM memory directly, raising the performance when transferring a large quantity of data.
On the first PCs there was a circuit in charge of such transfers called DMA controller. Originally this was an 8237 integrated circuit and then this circuit started to be embedded on the motherboard chipset, at the south bridge chip.
The PCI bus natively supports this feature – in this bus DMA feature is called Bus Mastering –, not needing any extra controller like in the old PCs. Any PCI peripheral can access the RAM memory directly if it wants to.