Both connect using a 40pin IDE ribbon cable, but there are two different cables.
There is a 80-wire cable that can be used for ata-100, ata-66 or ata-33 (or anything else that is IDE for that matter). This cable is required for ata-66 or ata-100 to help eliminate crosstalk at the higher speeds.
The other cable is a 40-wire cable that is used for ata-33 and below. It can be used for ata-66 and ata-100 but those devices will only work at ata-33.
You can tell an ata-66 cable by the fact that one end of it blue, the middle connector is grey, and the other end is black. On ata-33 the connectors are all the same color (usually black or sometimes grey).