Help ASAP building new pc what's this cable for??

Solution
The technical term is a molex connector to mini-molex connector for a floppy disk drive (normally). It is also called a berg connector - the smaller connector.

You do not need the cable at all unless you are using a floppy...which I hope you are not lol. Although some USB expansion bays require that mini molex connector.
The technical term is a molex connector to mini-molex connector for a floppy disk drive (normally). It is also called a berg connector - the smaller connector.

You do not need the cable at all unless you are using a floppy...which I hope you are not lol. Although some USB expansion bays require that mini molex connector.
 
Solution