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http://cablesaurus.com/index.php?route=product/product&product_id=28

So how do these work? Do you need to use these with crossfire or hwut?

The name implies what it does.  It is just an extender (or sometimes referred as a riser card) that allows you to add several cards onto your board and also give them room to breathe.  The one you listed has a Molex connector for added power when using a dual-GPU card or other power hungry card.

Here are some examples:

https://bitcointalk.org/index.php?topic=7216.msg1002670#msg1002670
https://bitcointalk.org/index.php?topic=7216.msg1003738#msg1003738

When would a person need to utilize the molex connector, would the cards not just pull any extra power needed from the 6 or 8pin power connectors?

I thought a card would first utilize the slot, pci express x16 for power then if the card is high power it would have the extra plug for you to add more power

in that case all cards WITH extra power plugs using the 1x to x16x extender would need the extra power connector assuming a 1x slot is less power than x16
and then only cards with no external power adapter at all MAY not need the extra power....

I believe the molex connector is for when you have more than four or five cards, to help supplement the power supplied by the mobo

Anyone know if there's a max cable length on these?  The ones I'm seeing aren't long enough for my purposes.. so I was thinking of connecting two together for each card.  Seem to be about 19cm in length each, so is 38cm too long?  anyone successfully done this?

Thanks

M

First, if you're going to buy the riser without molex 1x-16x, buy these: http://www.amazon.com/gp/product/B006DQRUZ8 (http://www.amazon.com/gp/product/B006DQRUZ8) , and thank me for your savings(I have 5 of those in my rig with 5830s, working fine for 2 months until now)

From what I know, the molex powered risers are for using more than 5 cards in motherboards that don't have a molex near PCI-E ports, like the one in the image. Most motherboards LACK that connector, so you'll need risers for more than 5 normal GPUs or you'll fry the 12V pins in the 24-pin ATX mobo connector.

http://img70.imageshack.us/img70/2483/17663124kz4.jpg

By normal GPU I mean 5830-like power consumption. With 5870s I think it's max 4 with unpowered risers per mobo. With 5970s and any DUAL-GPU card you NEED powered risers, or you'll fry the small 12V wires in the riser(they pull more power from the PCI-E slot).

With my Asrock Extreme4 970, I have 5 5830s with no powered risers, running fine.

With the riser length, I don't really know, and I can't find info online. You should buy the unpowered 1x-1x riser(http://cablesaurus.com/index.php?route=product/product&path=1&product_id=8 (http://cablesaurus.com/index.php?route=product/product&path=1&product_id=8)), and use it from mobo to the other riser. Then you should use the powered 1x-16x riser (http://cablesaurus.com/index.php?route=product/product&path=1&product_id=28 (http://cablesaurus.com/index.php?route=product/product&path=1&product_id=28)) from riser to GPU, to minimize heat and losses by wiring length.

I'm running 2x 5870, 1x 5850, and 2x 5830 in a rig with all unpowered risers.

The way it works is that each PCI-e slot supplies 25watts of power, and then from there 6-pin or 8-pin connectors add 75 or 150 watts respectively. So the power draw shouldn't be too great, but you have to make sure that your PSU has a pretty beefy 12v rail since the 25 watts for each slot is pulled from the 24-pin motherboard connector (~10.5 amps).