The cable looks much like a wide flat ribbon. When connecting drives to this interface, you must select the drive to be a Master, a Slave, or cable select which will assign either Master or Slave to a drive depending on which plug you use. Although it makes no difference in speed, some operating systems require you use Master for the primary bootable hard drive.
In the picture below, the IDE on this motherboard is number 10. The picture below that has the same board, just without the number so it's easier for you to see the interface. You can also click on the picture for a larger view.
I still use IDE for my DVD-Rom just because I had the drive kicking around. If you buy new, switch to SATA, you won't regret it.
Although this technology has been around for years, and is still on some new motherboards, it is obsolete as far as I'm concerned. Using a SATA is going to be faster, plus the whole Master, Slave thing is no longer required. It's much more plug and play.