How do I connect a slave hard drive to my desktop?

sata drives each need there own cable for data and power! if you have an extra sata connector on your motherboard then you can add another drive and if not you will need an ide drive if your board has one of those connectors? chances are if your board only has 2 sata connectors then the optical drive and the primary hard drive are already using them both? another thing you could do is buy a pci card with sata connectors on it? good luck!