GPU mining rig -- How much CPU is actually required?

[wndrbr3d]

Hello! I'm rather new to the bitcoin mining thing and have recently decided to spend the spare cycles on my primary desktop PC to earning something that would pay off.

I was pretty disappointed with my overall throughput (Q6600, 295 GTX) and was thinking that I could build a decent mining rig for < $500. Obviously the big part of the pie when it comes to computing is GPU, with CPU being the crumbly cookie crust if you choose to utilize it.

So my question is I'm thinking about building a GPU mining rig using a Radeon 5870 (or 5850) and hooking it up to a modest CPU/MOBO combo, like a Zotac ION ITX board. Would a dual-core Atom based PC be enough CPU to let a GPU miner reach full potential?

How much does the actual host CPU impact the GPU mining ability? My thoughts are that a dual core 1.6Ghz Atom running linux should have more than enough spare cycles to handle allocating GPU workloads.

Thoughts? 

[xaxistech]

Nope, I would recommend AMD though. You can get a AM3 board+dual core for $100.

[BinaryMage]

I think the Atom would have plenty of power, the GPU miner clients use barely any CPU at all. You can probably pick up a Sempron 140 and board for cheaper, though.

[Rob P.]

If the mobo will handle the graphics card, you can do it with anything.

However, I'd think building an Atom-based system would actually cost more than like an AMD Sempron Mobo combo.

I got my Mobo, CPU, RAM, and PSU for under $300.  I spent $300 on the GPUs.  The PSU is also going to be a limitation, as most Atom boards are low-power and therefore if they are bundled with a PSU, it'll struggle with the GPUs.

[kjj]

If you already have the case, PSU and flash drive, you can put together a single GPU box for about $100 + the cost of the GPU.

Used case with a crappy 250 or 300 watt PSU, a Gigabyte G31M-ES2L with a Celeron D CPU and some cheapass RAM.  The CPU only draws 35 watts max, so you can easily fit a 200 watt GPU onto whatever power supply you already have.

And if you have a bigger PSU, you can use a PCIe extender to hang a second card off it.

[wndrbr3d]

Ah! Thank you all for the recommendation of looking into Sempron boards vs. Intel Atom. I've been an Intel person for so long that I hadn't even considered that the AMD option (even going full Mobo+CPU) would be that much cheaper! Additionally, it seems for the same price point I'd have the option of going into a multi-GPU configuration as well going AMD.

The rig I have tentatively spec'd out is as follows:
- MSI 870-G45 AM3 Motherboard
- Sempron 140
- AMD 6870
- 2GB Crucial DDR3 1600
- Rosewill 430w 80+ Certified (no sense in wasting power)

The "out the door" price on this rig would be $430 from NewEgg. Using the ROI calculator over at bitcoinX.com, this seems like a no-brainer purchase.

Thoughts? (and thanks in advance!) 

[Yuvea]

alternatively to the sampron 140, you can get a x2 250 for about 60$.

[theunforgiven]

Sempron 140 is the best choice, but if you want to give a new "life" to that mining rig in the future, I recommend Athlon II series.

[tcpip4lyfe]

I just got a Sempron 140 for 30 bucks. Hopefully that will be enough.

[Soline]

Sempron 140 is fine and it save on power/money. You can always get better CPU later when you actually sell, depending on when you stop mining. There'll be new and better CPU you can put in, where an athlon might be useless by then.

[wildcard0]

How about pci-e bus speed?  Most video cards are x16, but often, you can get motherboards with slots that are mechanically x16 with only 4 or 8 actual pci-e channels.  Does the card do a lot of IO or is it a single function with a lot of GPU work using ram on the board?

Thanks

[kjj]

PCIe x1 is fine for mining.

[Rob P.]

How about pci-e bus speed?  Most video cards are x16, but often, you can get motherboards with slots that are mechanically x16 with only 4 or 8 actual pci-e channels.  Does the card do a lot of IO or is it a single function with a lot of GPU work using ram on the board?

Thanks

GPUs used for mining can go into x1 slots with extenders, so slot speed is not an issue.

Your biggest issue with a mainboard is having enough space between the PCI-E slots to allow for multiple cards and sufficient cooling.  Also, I'd actually think twice about a 430W PSU if you have a desire to do 2X GPUs on that board, especially 2x 6800s.

[honeybadger]

GPUs used for mining can go into x1 slots with extenders, so slot speed is not an issue.

Your biggest issue with a mainboard is having enough space between the PCI-E slots to allow for multiple cards and sufficient cooling.  Also, I'd actually think twice about a 430W PSU if you have a desire to do 2X GPUs on that board, especially 2x 6800s.

2 x 6800?

I have 2 x 8600GTS on an AMD64 X2....I considered putting it to work mining, but my reading led me to think my rig wouldn't cut it.

What do you think I could mine with it?

[Rob P.]

GPUs used for mining can go into x1 slots with extenders, so slot speed is not an issue.

Your biggest issue with a mainboard is having enough space between the PCI-E slots to allow for multiple cards and sufficient cooling.  Also, I'd actually think twice about a 430W PSU if you have a desire to do 2X GPUs on that board, especially 2x 6800s.

2 x 6800?

I have 2 x 8600GTS on an AMD64 X2....I considered putting it to work mining, but my reading led me to think my rig wouldn't cut it.

What do you think I could mine with it?

The rig I have tentatively spec'd out is as follows:
- MSI 870-G45 AM3 Motherboard
- Sempron 140
- AMD 6870
- 2GB Crucial DDR3 1600
- Rosewill 430w 80+ Certified (no sense in wasting power)

The "out the door" price on this rig would be $430 from NewEgg. Using the ROI calculator over at bitcoinX.com, this seems like a no-brainer purchase.

Thoughts? (and thanks in advance!) 

Yea, Radeon AMD 6870.  I was suggesting if he wanted to do 2X on that card, he'd need more power.

No, the 8600GTS is too old to be of use in mining at the current difficulty levels.  It would be better to scrap them and grab some 5770s at this point to get a decent Mhash rate.

[wndrbr3d]

Yea, Radeon AMD 6870.  I was suggesting if he wanted to do 2X on that card, he'd need more power.

Right, I got to thinking about that. A few sites that reviewed the 6870 showed the power consumption of 2x in Crossfire being around 390 watts in "benchmark systems", so I imagine this in case, running the Sempron buys me some overhead but that's too close for comfort. I'm thinking a 480w CoolerMaster would put me in a safer range... but it's not certified 80+.

I guess basically the point to my original thread was that when running a GPU rig, the CPU really doesn't matter. If anything, spending money on CPU for mining is pointless as the cost for performance between CPU's and GPU's is ridiculous:

~18 Mhash/sec for i7-980x ($1,099)
~300 Mhash/sec for 6870 ($199)

So for others that might have asked in this thread, I would say that any money spent on a CPU that's greater than a Sempron is just money wasted.