The P/N 1946-02R series cable is an enhanced IDE dual-drive cable, also
called Ultra ATA or Ultra 66 ATA. It's faster than a normal IDE cable, but
slower than an ATA-100 cable.
It is designed for high-speed IDE data traffic between one controller
card and up to two storage devices. Back in the day, this was the standard
method of connecting hard drives and optical drives to computers, but nowadays
you'd be hard-pressed to find a drive that uses this connector.
If you've just come across an old machine, though, this could be of use. Or if you're
building a time machine out of a DeLorean, these types of cables are commonly used
throughout such a rig. Couldn't tell you what for, but you can see them quite clearly.