Now, using a single PCI Express slot, you can add four external PCI slots - making system testing and card swapping convenient and less time consuming. Featuring a rugged steel housing to protect installed PCI cards, PEX2PCI4 supports both 3.3V and 5V cards, and includes the necessary PCI Express controller card to provide a connection between the host computer and the expansion unit that is as seamless as though the additional cards were installed directly on the motherboard.