Ultra 66 is fully backward compatible.
However it is still very new technology and  some drives on some ULTRA 33
controllers may give you problems. This is relatively rare. When this
occurs hard drive manufactures have a utility that will turn off ULTRA 66
and make the drive a ULTRA 33 until your ready to turn it back on.

m



>Will a Ultra DMA 66 hard drive work in a system that is only Ultra DMA 33
>capable? TIA.
>
>Reinaldo Rodriguez

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