IDE cables are designed to connect internal devices in your computer to the motherboard. The devices would include; CD-ROMs, Zip drives, hard drives, DVD-ROMs, CD burners, etc. IDE slots on the motherboard can only support up to 2 devices. Some IDE cables have more connectors. Those cables are for cases or situations where you need to have a longer cable or to have some variety and options to place the devices where you choose.
IDE slots on the motherboard can only support up to 2 devices.