The Word DMA (WDMA) interface is a method for transferring data between a computer (through an
Advanced Technology Attachment
Parallel ATA (PATA), originally , also known as Integrated Drive Electronics (IDE), is a standard interface designed for IBM PC-compatible computers. It was first developed by Western Digital and Compaq in 1986 for compatible hard drives and C ...
(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.
The WDMA interface is grouped into different modes.
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. This kind of transfer is implemented as "single mode transfer" in the
Intel 8237 DMA controller. In multiword transfer mode, once a transfer has begun it will continue until all words are transferred or the drive negates the DMA request line. This mode is implemented as "demand mode transfer" in the Intel 8237 DMA controller.
Two additional Advanced Timing modes have been defined in the
CompactFlash
CompactFlash (CF) is a flash memory mass storage device used mainly in portable electronic devices. The format was specified and the devices were first manufactured by SanDisk in 1994.
CompactFlash became one of the most successful of the e ...
specification 2.1. Those are Multiword DMA mode 3 and Multiword DMA mode 4. They are specific to CompactFlash. Multiword DMA is only permitted for CompactFlash devices configured in True IDE mode.
{, class="wikitable"
, + DMA modes
! Mode , , Max. transfer
rate (
MB/s) , , Bits , , Min. cycle
time (
ns) , , Defining standard
, -
, Single 0 , , 2.1 , , 16 , , 960 , , ATA-1
, -
, Single 1 , , 4.2 , , 16 , , 480 , , ATA-1
, -
, Single 2 , , 8.3 , , 16 , , 240 , , ATA-1
, -
, Multi 0 , , 4.2 , , 16 , , 480 , , ATA-1
, -
, Multi 1 , , 13.3 , , 16 , , 150 , , ATA-2
, -
, Multi 2 , , 16.7 , , 16 , , 120 , , ATA-2
, -
, Multi 3 , , 20 , , 16 , , 100 , , CompactFlash 2.1
, -
, Multi 4 , , 25 , , 16 , , {{080 , , CompactFlash 2.1
AT Attachment