Ultra DMA (UDMA) is the latest advancement to the ANSI ATA specifications. For detailed information see http://www.t13.org/. ATA-4, among other improvements, supports Ultra DMA modes 0, 1 and 2. UDMA mode 2 supports burst data transfer rates up to 33 MB per second (MB/s). ATA-5, among other improvements, supports Ultra DMA modes 3 and 4. UDMA mode 4 supports burst data transfer rates up to 66 MB/s.
ATA-5
Extensions
| Synchronous
DMA Mode for Ultra DMA |
| Mode |
Cycle Times |
Transfer Rate (Burst) |
| 01 |
120 ns |
16.6 MB/s |
| 1 |
80 ns |
25 MB/s |
| 2 |
60 ns |
33.3 MB/s |
| 3 |
45 ns |
44.4 MB/s |
| 4 |
30 ns |
66.6 MB/s |
| 1 - Equivalent to PIO mode 4
(ATA-3) |
UDMA/33 (ATA-4) doubles and UDMA/66 (ATA-5) quadruples the maximum transfer speed of the ATA-3 interface while maintaining the cycle time of the ATA bus clock at the rate used by PIO Mode 4.
This apparent miracle is achieved by:
Having the entity transmitting the data, either host or device, provide the clocking signal for the data
Using both edges of the clocking signal to strobe the data
For modes 3 and 4, improving the cable connecting the devices to the host.
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