The Word DMA (WDMA) interface is a method for transferring data between a computer (through an Advanced Technology Attachment (ATA) controller) and an ATA device; it was the fastest method until Ultra Direct Memory Access (UDMA) was implemented.
Single/Multiword DMA took over from programmed input/output (PIO) as the choice of interface between ATA devices and the computer.
In single transfer mode, only one word (16-bit) will be transferred between the device and the computer before returning control to the CPU, and later it will repeat this cycle even if the DMA request line is continuously asserted, allowing the CPU to process data while data is transferred.
Two additional Advanced Timing modes have been defined in the CompactFlash specification 2.1.
Multiword DMA is only permitted for CompactFlash devices configured in True IDE mode.