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.
thumb|80-conductor cable used for modes faster than UDMA 2 on the left compared to a 40-conductor cable
Modes faster than UDMA mode 2 require an 80-conductor cable to reduce data settling times, lower impedance and reduce crosstalk.
thumb|[[SanDisk 32 GB CF card supporting VPG20 and UDMA7]]
{| class="wikitable" style="text-align:center"
|+ Transfer modes
! Mode || Number || Also called || Maximum transfer<br/>rate (MB/s) || Minimum<br/>cycle time || Defining<br/>standard
|-
| rowspan=8 | 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 || || 44.4|| 45 ns || ATA-5
|-
| 4
|}
See also
- PIO—The first interface type used between devices (mainly hard disks) and the computer.
- Parallel ATA
- Serial ATA