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.
DMA Mode for Ultra DMA
||Transfer Rate (Burst)
|| 80 ns
|| 25 MB/s
|| 60 ns
|| 45 ns
|| 30 ns
|1 - Equivalent to PIO mode 4
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.