You can add a PCI IDE controller, or RAID controller to your computer. That would give you 2 additional channels with 2 devices per channel.
computerdag
My motherboard, like a lot of others has two IDE ports, both of which have two lots of hardware attached, how do I add yet more? I have two hard drives attached to one and one cd-rom and one zip drive on the other and I wish to install a new DVD drive.

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