They are the same thing. They have different modes, so you will need to know what your motherboard supports. The drives are all backwards compatible to the older speeds.
ATA/DMA 33 - UDMA Mode 2, ATA/DMA 66 - UDMA Mode 4, ATA/DMA 100 - UDMA Mode 5, ATA/DMA 133 - UDMA Mode 6
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