Ultra Direct Memory Access (Ultra-DMA)
The latest improvement of the EIDE device interface. Also known as ATA/ATAPI-4, Ultra-ATA, or Ultra-DMA/33, this is the latest advancement to the ATA specifications (draft): ATA/ATAPI-4. Which, among other improvements, supports Ultra DMA. This interface has a theoretical maximum data transfer rate (burst, not sustained) of 33MB/sec. Maxtor drives that support Ultra-DMA will have a suffix of "D" instead the traditional "A".
Ultra-DMA doubles the maximum transfer speed of the ATA-3 standard. Compare the Ultra DMA maximum burst transfer rates with the old ATA standards above.
ATA-4 Extensions
Synchronous DMA Mode
for Ultra DMA/33 |
| Mode |
Cycle Times |
Transfer Rate |
| 0 |
235ns |
16MB/s |
| 1 |
160ns |
24MB/s |
| 2 |
120ns |
33MB/s |
As you can see, Ultra DMA/33 achieves nearly double the transfer rate of the existing ATA interface while not increasing the cycle time of the ATA bus clock over the rate currently used for PIO Mode 4.
This apparent miracle is achieved by:
-
Improving timing windows in the protocol on the ATA bus;
-
Reducing propagation delays by pipelining data transfers;
-
Transferring data in synchronous (strobed) mode;
In addition, Ultra DMA/33 improves data integrity by using a Cyclic Redundancy Check (CRC) to flag any data transfer errors that may be made over the ATA bus (Note: In this application CRC is only used to improve data integrity for ATA bus transfers, it is not used to improve the data integrity of either disk drives or host systems). Ultra DMA/33 requires no physical change to the cable, receivers, or drivers of the ATA bus. Furthermore, Ultra DMA/33 protocol and commands have been designed to be compatible with existing ATA devices and systems. Thus, new Ultra DMA/33 devices will be backwards compatible with most older (non Ultra DMA/33) systems. Older ATA-1/2/3 devices will also be forwards compatible with systems that have Ultra DMA/33 capability.
All current Maxtor devices now support Ultra DMA/33. Please see our Ultra DMA FAQ for more details and where to find Ultra DMA Adapters.
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