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The Ultra DMA (Ultra Direct Memory Access, UDMA) modes are the fastest methods used to transfer data through the ATA hard disk interface, usually between a 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.cite-ref-1[1]

| Mode | Number | Also called | Maximum transfer rate (MB/s) | Minimum cycle time | Defining standard |

|---|---|---|---|---|---|

| Ultra DMA | 0 | | 0 16.7 | 120 ns | ATA-4 |

| Ultra DMA | 1 | | 0 25.0 | 0 80 ns | ATA-4 |

| Ultra DMA | 2 | Ultra ATA/33 0 | 0 33.3 | 0 60 ns | ATA-4 |

| Ultra DMA | 3 [ 2 ] | | 0 44.4 | 0 45 ns | ATA-5 |

| Ultra DMA | 4 [ 2 ] | Ultra ATA/66 0 | 0 66.7 | 0 30 ns | ATA-5 |

| Ultra DMA | 5 [ 2 ] | Ultra ATA/100 | 100 .0 | 0 20 ns | ATA-6 |

| Ultra DMA | 6 [ 2 ] | Ultra ATA/133 | 133 .0 | 0 15 ns | ATA-7 |

| Ultra DMA | 7 | Ultra ATA/167 | 167 .0 | 0 12 ns | CompactFlash 6.0 [ 3 ] |

• See also

• References

• PIO—The first interface type used between devices (mainly hard disks) and the computer.

• Parallel ATA

• Serial ATA

cite-note-11. ↑ AT Attachment with Packet Interface - 7 Volume 2 - Parallel Transport Protocols and Physical Interconnect (ATA/ATAPI-7 V2) E.2.1.1 Cabling p172

cite-note-80c-21. 80-conductor cable required

cite-note-32. CompactFlash 6.0 Introduction Archived 2010-11-21 at the Wayback Machine