Originally Posted by yee245
is there any reason that you can't make a wire (it would be very thick) of shielded wires that would just be kind of like an extension cable to the PCIe slot on the mobo? i mean, would there be that much of a slowdown, assuming the wires were not significant resistance and such, and no interference between the wires (the reason for say shielding each of them), and it would technically be as if it were connected directly to the mobo. or, would like a foot or two worth of that cable have enough resistance that you'd have to supercool it to be efficient?
I don't think that resistance would be the problem - it'd be timing. Most standards (PCIe, PCI, IDE, and USB for example) have a maximum length limited by the signal timing. This is more of an issue with high-speed data transfers. The official limit for USB devices is 5m, or 3m for keyboards/mice, regardless of how good the cable is. Using a hub/repeater will extend the distance.
Even USB only manages about 480Mb/s = 60MB/s. Compare that to PCIe 16x, which manages 4GB/s in each direction, and it becomes clear that external interfaces have a long way to go.
Quite apart from that, there's the power considerations. If the laptop doesn't provide power, you can only use the external video card while it's plugged in somewhere. If the laptop does provide power, it has to provide a lot
of it - at least 100w for modern cards. I think some are rated at ~140w (the Geforce 7950GX2s). That'll require serious power regulation circuitry in the laptop, very thick cables, and a ridiculously powerful battery.
There's also the issue of size and weight. Normal video cards aren't built for low-weight or small size. They're built for good cooling and performance. Would you really want to carry a second box containing a video card with a rather hefty heatsink everywhere you went?