The Ultra DMA (UDMA) interface was the fastest method used to transfer data between the computer (through the ATA controller) and an ATA device until Serial ATA. UDMA took over from Single/Multiword DMA as the choice of interface between ATA devices and the computer. The UDMA interface is grouped into different modes ranging from 0 to 6 each with its own specifications.

Transfer Modes
Mode Number Also called Maximum transfer
rate (MB/s)
Defining standard
Ultra DMA 0 16.7 ATA-4
1 25.0 ATA-4
2 Ultra ATA/33 33.3 ATA-4
3 44.4 ATA-5
4 Ultra ATA/66 66.7 ATA-5
5 Ultra ATA/100 100 ATA-6
6 Ultra ATA/133 133 ATA-7
7 Ultra ATA/167 167 CompactFlash 6.0