This cable is suitable for connecting either one or two IDE hard disks to a desktop computer, using the primary or secondary IDE socket on the motherboard.
The cable is compatible with any current or ancient IDE speed (66MHz, 100MHz or 133MHz) and works without any problem with my Intel 815 Chipset, on a 1999 motherboard which supports 66/100/133MHz on the front side bus (FSB).
You're typically going to buy this cable to replace an old one that's faulty, or to replace one that only has a single connector (so can only connect one hard disk) with this one which can connect two.
Although it's is an 80-wire cable, 40 of those wires are earth wires (i.e. they're grounding, or shielding, the 40 wires that carry data, in order to improve the reliability of the connection, in the face of electrical interference from other signals inside the computer). So what you'll actually see is a 40-pin connector, not an 80-pin one.
Take proper anti-static precautions before opening the case on your computer. Static electrical charges on your clothes and hands can fry the delicate electronics inside the case - beyond repair!
The cable connects to the Primary IDE connector: the 40-pin blue connector on the cable plugs into the motherboard's primary IDE socket (which is also blue).
Note: Your CD-ROM, or DVD-ROM, will be plugged into the board's other (secondary) IDE connector, using a similar ribbon cable. Don't unplug that device! (If you do, it's too easy to become confused as to which ribbon cable attaches to which socket on the board).
The black connector on the cable (the one at the end of the cable) plugs into the 40-pin connector on your hard disk. If you're only attaching one disk to this cable it MUST be attached to the black connector. This disk will normally be your Drive C: (containing the operating system, e.g. Windows or Linux). This is known as the "primary master" disk.
Optionally, if you choose to attach a second hard disk, the grey connector on the cable (in the middle of the cable) plugs into your second hard disk. This is known as the "primary slave" disk (if present), and it need not be bootable.
A hard disk has a "hardware jumper" block, located next to its 4-pin power connector. The safe choice for this is to set the tiny jumper pin (on all of your hard disks) to the "cable select" position: follow the printed instructions on the hard disk's label. Using that setting can avoid a good deal of useless problems and complications.
Once your new IDE cable is connected up, remember to re-connect any cables which you had to temporarily disconnect during the fitting process (e.g. the hard disk's 4-pin power connector).