Quite simply, because risers have a fixed length and the cards would only extend a few inches above the mobo anyway and the longer you make them, the less likely the cards will hash properly or even be detected by the mobo. I read somewhere on this forum that 30cm's is the limit to a PCI-E riser cable. Anymore and the resistance is too great and the card underperforms or fails to be detected. Some people have reported success in daisy chaining a couple together, tho personally my powered risers wouldn't allow the PC to boot if I daisy chained them (2 x risers together). My risers are about 18.5cm long each from tip to toe so going by the 30cm rule, it made sense that the cards failed to initialize correctly despite powering up. This and the fact I'd get ALOT more air flow if i had everything out of the constraints of the case with proper spacing.
Very good points! Theoretically though if you had a shelf inches away you might be able to get away with a 12" Riser coming from the case but then again probably not with it already sunk inches in. So yes..here what your saying and pretty sure I am going to have to take apart an older computer to make that happen. Might not be able to put it back in if I ever wanted to
As for the differences? Well, I'm no expert and without googling the actual answer I'd hazard a guess that it's just transfer rates and shouldn't impact mining speed whatsoever since it's the GPU's themselves that are doing the computations. There is actually a thread or two talking about this since there are a few people wondering how long you can make a riser cable. Maybe someone more knowledgeable in this area could chime in but for the most part, I'd already ordered x16 risers so I chose to stick with them for now. I still have another 2 x4 PCI-E slots available and 2 x1 slots on my mobo for future expansion should I decide to go that route. Having said this, I tried to throw in an old 5770 (flashed to a 6770) in one of the PCI-E x4 slots and both my 7970's hash rate dropped to ~500kh/s. I haven't investigated this any further as of yet but plan to see why this happened eventually.
As a side note, moving air cools and stays cool alot quicker than still air. So as long as you have some kind of air movement along with everything out of the case, then temps will be a non issue for the most part. Infact, take a look at the
https://bitcointalksearch.org/topic/--7216 thread. Lots of mining rigs there both open case, rack mounted or full tower setups. I go jelly when I view that thread
Thanks for that link! huge help in seeing what everyone else is coming up with and pretty sure i am ready to make my home depot and frys trip soon. As for the 1x and 16x it looks like it really doesn't make too much of a difference from my readings due to amount of power/memory?something? not needed but testing will be a whole nother story as nothing is every as easy as it sounds. Luckily I only need 1 or 2 x16 as the 1x seems to come in handy when trying to connect more then 2 GPU's. I could be mistaken though. I have an old 5770 on my Mac Pro but couldnt get it above 50 kh/s no matter what I did. Instead it spits 160 mh/s for BTC which isnt much but can leave it on over night to gain 60 cents..ha!
So pretty happy just rolling with my steady 700 kh/s right now on a 925/1275 & tc8192 with temp 82-84 until I can bring it out of the case and ramp it up higher. On a 1045/1500 it shoots way past 750 kh/s now but temps creeping past 88/89 so I think I can live with 700 being in a metal heat box. Pretty sure if i keep it below 85 no damage will be done right? Thanks again for the advice..feels lovely to be collecting coins now..ahhhh