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The Ultra DMA (Ultra Direct Memory Access, UDMA) modes were the fastest method used to transfer data through the ATA hard disk interface, usually between the computer and an ATA device. UDMA succeeded Single/Multiword DMA as the interface of choice between ATA devices and the computer. There are eight different UDMA modes, ranging from 0 to 6 for ATA (0 to 7 for CompactFlash), each with its own timing.

Modes faster than UDMA mode 2 require an 80-conductor cable to reduce data settling times, lower impedance and reduce crosstalk.[1]

Transfer Modes
Mode Number Also called Maximum transfer
rate (MB/s)
cycle time
Ultra DMA 0 16.7 120 ns ATA-4
1 25.0 80 ns ATA-4
2 Ultra ATA/33 33.3 60 ns ATA-4
3[2] 44.4 45 ns ATA-5
4[2] Ultra ATA/66 66.7 30 ns ATA-5
5[2] Ultra ATA/100 100 20 ns ATA-6
6[2] Ultra ATA/133 133 15 ns ATA-7
7 Ultra ATA/167 167 12 ns CompactFlash 6.0[3]

See also[edit]