Questions about my Mining Rig

[Monty Carlo]

I am new to building computers (I've always been on the software side of computer science), so I would appreciate your advice on my bitcoin mining rig. I also have a few lingering questions.

For reference, I've created a list of the components:

Motherboard: ASRock 970 Extreme4
Power Supply: OCZ ModXStream Pro Power Supply - 700-Watt??
CPU: AMD Sempron 145
Memory: Mushkin Enhanced Essentials 2GB
Video Cards: Sapphire Radeon HD 5830 (x3)??
Tower: NZXT Technologies Source 210 Computer Case
*I will be running from either a flash drive or the hard drive from my old computer

I do apologize in advance if these questions have been asked/answered already.

1) This motherboard has 3 pci-e (x16) slots, so if I use 3 graphics cards, will they fit right? Is it possible that there will be a spacial issue on the board, trying to get the cards not to run into each other, and if so, is there a fix?
2) Is a 700-watt power supply sufficient to power these graphics cards? If anyone has experience with these particular cards, your insight would be most helpful.
3) Will the mining software (I use GUIMiner) detect each graphics card separately and divide the work? I hear crossfire is not very effective.

Thanks for your help!  

EDIT: Oh, and will the traditional cooling practices work fine?

[FbBitcoinLottery]

a lot of people wedge things between the chips... there shouldnt be any problems with them touching... only issue is heat trapped between...

[kwoody]

The cards should fit fine, but it may be a tight squeeze, and this would lead to heating issues(middle card running especially high temps). If this is the case, get a riser/extender for the middle card, and the top/bottom cards will have ample breathing room.

700w *should* do it, but it's cutting it awfully close. Some of my cards are 5830's, and they draw right around 200w. Be sure to underclock the memory, as GPU memory clocks don't affect hashrate. If you can, run your OS off a thumb drive to give your 700w PSU a little more room to work with, last time I checked, mechanical spinup hard drives can draw about 40w. Avoid using an optical(dvd-rw rom) drive if you can, this will also save you power. You should be fine if you boot from flash/SSD, use a single stick of RAM, and underclock the memory on the cards. Will be close though. Also very important that the PSU has enough Amps running on the 12Volt rail to power the cards. Not sure what the minimum is, but 5830 will run just fine on 18 amps, and alot of PSU's will have multiple 12V rails with 18 amps.

Your cards should get detected fine without crossfiring them if you're using Linux, no special trickery needed. My rigs are running Winblows, and as of last year, I had to/still am make use of VGA "dummy plug"s where you trick your extra cards into thinking they have a display/monitor plugged into them. Involves plugging resisters into specific pins on a VGA adapter; process explained here:  http://www.overclock.net/t/384733/the-30-second-dummy-plug . Not sure if this is still necessary, but I'm still using them. Crossfire will gimp your hashrate by about 10% per card.

Good luck!

[Monty Carlo]

Ah, ok I'll probably get risers for the middle card and as for the power supply... sigh* I think i'll just upgrade it. I really don't want to risk it. Besides, what if i decide to overclock, that would definitely now work out. Thanks for the help, both of you!

[Gabi]

Please note 2 things
1)Bitcoin is not a get rich quick scheme
2)Soon ASIC will be released and they will be dozen of times faster than your computer. Even todays FPGA are better....

[Monty Carlo]

Yes, I understand this. I am doing this for 3 reasons:

1) Like I said, I'm a computer science major. It sounds like fun!
2) I get free electricity, so once I cover the costs of the build, its only profit (possibly)
3) I was able to find really good deals on everything.

Thank you for your concern though.

[kwoody]

So I was looking up some geeky hardware stuff on overclock.net and came across some info on the 5830. At stock GPU/memory clocks, the max TDP for 5830 under 99% load is 175 watts. So...

1x Sempron 45w CPU
1x stick of RAM, maybe 2-3w?
1x USB stick, another 2-3w maybe
1x Motherboard power, maybe 20-30w?
3x Radeon 5830, 525w

You're probably fine with that 700w. How many amps on the 12Volt rail and how many seperate rails? Underclocking the memory should cancel out overclocking the GPU..? Your setup should be pulling around 600w from the wall.

[Monty Carlo]

The 700 watt one had 2 rails @ 25 Amps each for a total of 50 Amps. The number of rails don't matter as long as the total is enough, right? Even so, 50 probably would't be enough. But at this point, I'm considering getting a 850-watt PSU instead. I really don't want there to be even the possibility of the thing frying my machine (esp. while I'm away).

EDIT: Can I have your opinion on this 750 watt PSU?
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=927378&csid=_61

[kwoody]

That PSU should definately do the trick. After doing the math on the 5830's, the 175watts they draw equates to just under 14.6 Amps each. That PSU has the ideal single 12V rail. You should be good to go with it.