I have read the wiki section about the usb port issue. I am currently experiencing with a 4 webcam system, but thinking about upgrade it to 6-8 cameras as I need to do some two people capturing. My computer got 2 on board usb 2.0 (2 ports front and 4 ports behind) and one usb 3.0 (two ports behind). See the attached image for the screenshot of the hardware manager. It looks like the chipset of usb 3.0 is one of the μPD720202, μPD720201, μPD720200A. According to the wiki, they should not have problem with sony ps eye camera (even they have slightly higher frame drop rate than the other two usb 2.0 in practical).

Now as I may test the recording system on more than one computers, I want to use a 4 ports usb 3.0 hub to link more cameras than put a PCI-E card in one computer. The USB 3.0 have up to 5G transfer rate. In theory the hub and the usb port could handle 4 cameras. However, after 4 cameras were linked to the usb hub, both of them suffers a horrible frame drop rate. Could I ask why dose this happen?....If I want to put 8 cameras on the computer, should I buy another PCI-E card for usb 3.0?

PS Eye cameras are USB 2.0 devices, thus they work with USB 3.0 controllers in compatibility mode, and cannot utilize full USB 3.0 bandwidth. In case you just want to test tracking with the greater number of cameras, you can connect more than 2 cameras to a single USB controller if you reduce the frame rate.

To support 8 cameras at 60 fps, 4 USB controllers are needed. In your case that means one additional PCIe card (or two, if built-in USB 3.0 continues to suffer frame drops).

Thanks a lot that's very clear. I only have one spare PCI-E 1X slot on my mother broad. I think I only can expand it to 7 as the existing usb 3.0 is not very stable.