This item is from the Yet Another Enhanced IDE/Fast-ATA/ATA-2 FAQ, by John Wehman and Peter den Haan with numerous contributions by others. (v1.92).
Ultra-ATA is somewhat similar to Ultra-SCSI in the sense that it bridges the gap between the current standard (ATA-3) and ATA-4, which isn't quite finished yet. Ultra-ATA adds a new, high performance mode: DMA/33 with 33MB/s bandwidth, twice that of DMA mode 2. It is supported by Intel's Pentium II chipset, the TX Pentium chipset, the latest Intel competitors and a few add-on (PCI) cards.