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The original EIDE interface allowed for a maximum data transfer rate of 16 megabytes per second (MB/sec). The next data transfer improvement was accomplished with the introduction of the Ultra DMA or Ultra ATA interface. This is an interface patented by Quantum but supported by all motherboard and disk drive manufacturers. The technology involves an improvement in the governing electronics that deliver the hard disk data to the system board. Quantum succeeded in reducing the bottleneck that occurs in transferring data to/from the EIDE hard disks. The UDMA hard disk is no faster, but the data paths have been optimized. With the new protocol, the speed is doubled by allowing twice the data transfer per clock cycle. This is referred to as UDMA/33 (UDMA mode 2) and supposedly has a maximum data transfer rate of 33MB/sec. However, in practice, this maximum speed is rarely achieved.

In 1997-98 Intel and Quantum created another Ultra DMA standard called ATA/66 or UDMA/66 (UDMA mode 4). This protocol has a theoretical bandwidth of 66MB/sec. It also requires a cable with 80 conductors instead of the original 40. The 40 additional conductors are used for grounding. In the older cables, only seven conductors were used for grounding. This improved grounding removes the noise remaining in the cable after a transmission (crosstalk). In the UDMA/33 protocol the controller had to wait for noise in the cable to disappear before the next transmission. With the new cables the noise is dramatically reduced, so there is less delay in data transmission.
In spring of 2000, the IBM hard disks became so fast, that UDMA/66 became inadequate. These fast disks use a protocol called UDMA/100, developed by Quantum, who holds the Ultra DMA patents. Where UDMA/33 gave a very powerful boost in the bandwidth between controller and hard disk, UDMA/66 gives less of a gain in performance. On the other hand it solves a lot of compatibility problems by improving timings and other parameters in the UDMA specification. The UDMA/100 specification is reportedly simpler to implement in the chipset logic. Therefore it is cheaper to produce and fully compatible with both UDMA/33 and UDMA/66. It also provides another significant increase in hard drive performance.

The UDMA/100 interface has a theoretical bandwidth of 100MB/sec. This is more than any hard disk can deliver at present. However, the hard disk technology is improving rapidly, so disks may soon reach this limit. When that occurs, further improvements in data transfer technology will be needed. That new technology may be Serial ATA. Intel, Dell, IBM, Maxtor, Quantum and Seagate, and other partners are about to replace UDMA/100 with this new interface. The Serial ATA interface can transfer data at a rate of 160MB per second in its initial version (Serial ATA 1X or SA1X). Later versions are expected to provide bandwidths of up to 528MB per second. This will give us room for the next five years of hard disk technology improvements. It may also put the IDE technology ahead of SCSI for the first time.