Topic: Newbie hardware question, specifically Risers and PCI-E modes (Read 851 times)

Thanks for your reply!

I completely agree that the i5+SSD is total overkill with this setup, but it's what I have at the moment. I have an unused machine with a small SSD, windows 7 64 bit installation, an 800W PSU and the BPU/Mobo/RAM. So I might as well put it to work. If it looks like I'm going to be able to get my money back on the first couple of cards, I'll buy components for a lower power Mobo/CPU setup in about a month. For starting, I'm going to have a punt on 2 cards only. I'll add more if it's working profitably.

Riser wise, what I'll do at the start is go with one 16x-16x powered and leave the other card on the board.

Looking forward to getting started

Rit.

Whether we're talking SHA 256 or scrypt algorithms and probably whatever else becomes popular for GPU mineable alternative coins in the future, we tend to see a tiny amount of data, that make for HUGE amounts of work and product a small answer. Therefore external data bandwidth is not all that important. For an SHA example the BFL bitforce 60Gh single uses a serial to USB conversion chip internally so data throughput would be throttled at something like 115,000 bits per second.

Now there's two things that can make a card work or not work with a particular riser (or slot if a full length 4x or similar). One is power, the second is the negotiation or lack thereof of the PCIe channel width.

PCIe cards have 4 pins which are used to detect what the device is capable of, at various lengths along the connector, relating to length of standard slot size for each speed, there's a 1x pin a 4x pin an 8x pin and a 16x pin. As you might guess the 1x is near the front, the 16x is near the back. The card is supposed to short these to say what bus width it will use. On some cards the 1x and 4x are not connected, so the card does not signal the motherboard that it is there or can use 1x or 4x. In this situation the 1x pin can be manually connected to the sense pin to force things into 1x mode. It can vary what works with one model of card on one motherboard vs same card on another motherboard.

The other variable, power depends again on card and motherboard. If the card is absolutely relying on sucking 75W out of the motherboard, then a powered riser will make it work, (With a molex connector on it) where an unpowered riser won't. Some motherboards want to supply 75W, but the onboard distribution is insufficient to allow this. OR in the case of multiple rail supplies the 12V from the ATX supplementary connector may only supply 200W or something and get overloaded quick. Some, mostly older motherboards had a molex socket on for additional PCIe power.

In your particular case, since you have 3 full length slots on your motherboard, and plan only 3 GPUs at this point in time, then it's possible that you could run all three on the board. This only works with GPUs that have blowers rather than fans, since blowers have high static pressure and can actually suck in enough air with only a 1/4 inch gap between cards. With fan based cooling systems they would overheat quick. Some people prefer the quieter whoosh of a fan based cooling system rather than the howl of the blowers (Which are gonna pretty much run near full speed all the time when the GPU is in constant use) IF you decide to go this route, have a high power side panel fan blowing right on top of GPUs, and also front fans, to get the most possible cool air into their vicinity, have more CFM going in than out the rest will be forced out through the GPUs.

If you can only get the fan based cards, I think really you can manage with only one 16x to 16x riser at the moment (Powered if you want insurance) unless you want to build a framed out rig now for adding extra GPUs on 1x to 16x risers later.

You may or may not have a problem with the GPU in the 4x slot, one solution may be to connect the 4x presence detect pin to the signal pin with conductive paint or pen.


Two other things about your proposed configuration stand out, the i5 CPU is overkill as is the 64GB SSD. If you have not purchased these, don't. The SSD does have a small power saving advantage, but you can boot linux off a regular USB stick for dedicated miners, so the cost/benefit of SSD is worse. The i5 will probably cost you 50W of power useage more than you need to just run the miner, also makes 50W more heat than you want kicking around in there, compared to more basic CPUs you could run in this board. Also removes 50W of power from the motherboard power budget. Not sure what the market for them is like over there, but it's potentially possible that you could sell it, buy a cheaper one and have at least 50 quid more to apply to rig or save. A reason for keeping the i5 would be that you can defray it's power cost by mining CPU coins on it (Primecoin, protoshares, quark, molecules etc) One of my rigs has a celeron 440 underclocked to 600Mhz, even then cgminer only uses about 15% CPU.

Oh in case you didn't see it anywhere yet, don't use crossfire bridges.

Hi all!

As this is my first post, this is the only forum I can post in, so apologies if this is an inappropriate place for this query.

So, like alot of people at the moment, I'm going to have a punt for a few quid at GPU mining (not Bitcoin, most likely Litecoin). I've been putting together a shopping list, and given the hardware I already own, I'll be buying:

3 x Radeons (probably 7950s, maybe R9s, will have to see how healthy the bank account is )
1 x PSU (1200W Platinum)

These will be used with an old Asus p8-p67Pro that I have spare, and I'm trying to pick the correct risers to use. According to the motherboard manual, I have:

2 x PCI-E 2.0 x 16 slot (single at x16 mode, dual at x8/x8 or x16/x1)
1 x PCI-E 2.0 x 16 slot (at x4 mode)
1 x PCI-E 2.0 x1 slot

I had planned to grab some x16-x16 risers, but what is throwing me here is the mode. Does it matter? If not, I can just buy 3 16x-16x powered risers and that's it, right? If it DOES matter, could someone drop a hint on me about which are the correct risers to get.

Sorry if this is a really stupid question, but I have never run a machine with more than one GPU before, and mode is not something I have fallen foul of before.

Thanks!

Rit.

PS: I doubt it matters, but the overall rig in the end will be 3 x Radeon, i5-2500k, 8GB RAM, 1200W Plat PSU, 64GB SSD, Win7 64-bit on an Asus P8-P67 Pro (MicroATX)